At its core, this tool answers one question as honestly as possible: if you retire with the money and choices you actually have, how likely is it to last? You build a real portfolio, set your real numbers, and it stress-tests the whole thing thousands of different ways instead of giving you one falsely-precise answer.

A few things make it worth using rather than a back-of-envelope guess:

• It tests your plan two genuinely different ways — a 2,000-path Monte Carlo simulation using current, real capital market forecasts (not stale historical averages), and a Historical Stress Test that replays your exact plan against what actually happened in the market from 1995 through 2024, including the 2008 crash, the 2020 COVID crash, and 2022. Most simple calculators only do one or the other, if either.

• The tax math is real, not a flat guess. Federal brackets, standard deduction, Social Security's actual partial-taxability formula, Required Minimum Distributions with the correct IRS divisor table, Medicare IRMAA surcharge tiers, and a real per-state tax rate for all 50 states — computed year by year, not approximated with one made-up percentage.

• It handles real households, not just a single simple case. A spouse with their own Social Security, their own separate 401(k) with correctly independent RMD timing, a pension, charitable giving, Roth conversions, an existing Roth balance, a taxable brokerage account, cash reserves — all optional, all interacting correctly with the same tax engine at once.

• You choose how you actually want to spend in retirement — a fixed inflation-adjusted income, a dynamic percentage of your balance, or the published Guyton-Klinger guardrails strategy — rather than being locked into one assumption.

• It's built to be checked, not just trusted. Every number has a tooltip explaining exactly where it comes from and what it assumes, the footnote spells out every simplification and limitation in detail rather than hiding them, and you can print a clean summary report to keep or share. This tool would rather tell you what it doesn't know than quietly guess.

No tool like this is complete, and the honest list of what's missing or simplified matters as much as the list of what's included. Here's the real picture, grouped by what kind of gap it is:

The future is genuinely unknown

• Return assumptions are current professional forecasts (Vanguard, BlackRock, Fidelity, Invesco), not guarantees — actual returns over your real 30+ year retirement could land well outside these ranges in either direction.

• The Historical Stress Test only has real market data from 1995–2024. It captures the dot-com crash, 2008, and 2022 — genuinely bad sequences — but it can't include the 1973–74 bear market or the 1966–1982 stagflation era, which some published research considers an even worse historical retirement start than 2008.

Real costs this tool doesn't model at all

• Long-term care costs — a major, unpredictable expense for many retirees, not included anywhere.

• Annuities or other guaranteed-income products — you can't test "what if I bought an income annuity with part of this."

• ACA marketplace subsidies — the pre-65 healthcare bridge cost is a flat number you enter, not income-adjusted the way real subsidies are.

Simplified on purpose, to keep the tool usable

• Your allocation stays fixed for your whole retirement — no gradual shift toward bonds with age, no rebalancing mechanics.

• State tax is one estimated rate per state, not full bracket-by-bracket modeling — accurate enough for planning, not for a real filing.

• If your spouse has their own retirement account, this tool correctly forces their legally-required RMD at the right age — but it doesn't optimize which spouse's account to draw from for everyday spending the way a real couple might.

• Medicare IRMAA uses your same-year income as an approximation; the real rule looks back two tax years.

Fund scoring is cost/risk-based, not a full manager evaluation

• The Score column reflects expense ratio, estimated risk-adjusted return, and diversification value — it does not include fund-specific alpha, upside/downside capture ratios, or manager tenure, since those require research this tool can't verify on its own.

• Above all: this is an educational planning tool, not personalized financial or tax advice. It wasn't built by a licensed financial advisor or CPA. Use it to understand your own numbers and compare choices — bring the real decision to a professional, especially anything involving taxes, Social Security claiming strategy, or Medicare timing.

This is the "under the hood" explanation — not what each field means, but how the tool actually gets from your inputs to the numbers you see. Five things are worth understanding.

1. The Monte Carlo method — 2,000 random futures, not one guess

Nobody knows what the stock market will actually do over your retirement. So instead of picking one assumed return and running the numbers once, the tool generates 2,000 separate, independent simulated futures. Each one draws a random annual return for every single year of your retirement, based on your portfolio's expected return and volatility (its "expected value" and how much it typically swings) — some years land better than expected, some worse, mostly clustered in between, the way real markets behave. Your Success Rate is simply: out of those 2,000 attempts, what percentage never ran out of money.

2. How a withdrawal amount actually gets calculated each year

This is more involved than it looks. You don't just tell the tool "withdraw $60,000" — you tell it "I need $60,000 to actually live on, after everything." So each year, the tool works backward: it estimates a withdrawal, calculates the real federal tax, state tax, Medicare premium, and any early-withdrawal penalty that withdrawal would trigger, checks whether what's left over (plus your Social Security and any pension) actually equals your spending target — and if not, adjusts the withdrawal up or down and checks again. It repeats this a handful of times until the numbers land correctly. That's why your "Portfolio Withdrawal" in the yearly table is usually noticeably bigger than your spending target minus Social Security — it's been "grossed up" to cover the taxes on itself.

3. What "15th percentile," "median," and "90th percentile" actually mean

These are not three specific simulated paths you can follow start to finish. For every single year, the tool looks across all 2,000 simulations and asks "what balance falls at the 15th-worst position this year, across all of them" — then repeats that question independently for every other year. This is the standard, correct way to summarize thousands of random outcomes, but it means the "Bad Luck" line isn't one continuous story of one unlucky retiree — it's a year-by-year snapshot of "how bad does the 15th-percentile outcome look at this particular point in time." For most purposes this distinction doesn't matter, but it explains why some numbers in the Year-by-Year table (like the Withdrawal Rate or Guardrails spending amount) are tracked and reported a little differently than you might expect.

4. The Historical Stress Test works completely differently — no randomness at all

The Monte Carlo above is entirely random. The Historical Stress Test is the opposite: zero randomness. It takes the real, actual S&P 500 and bond returns from 1995 through 2024 and simply replays your exact plan starting from each of those 30 real years in sequence — including what genuinely happened in 2008 and 2022. There's no "15th percentile" here because there's nothing random to rank; each of the 30 rows in that table is one specific real year in history, not a statistical summary.

5. The order money actually gets spent from, if you have more than one account

If you've turned on Other Assets, the tool doesn't just lump everything into one pile. Every year, spending is covered in a specific, deliberate order: Social Security and pension income first (since that money arrives regardless), then cash, then your taxable brokerage account, then your main 401(k)/IRA/Roth portfolio, and finally any additional Roth balance as an absolute last resort. This isn't arbitrary — it's the standard, tax-efficient order real retirement planners recommend, since it lets your most tax-advantaged money (Roth) keep growing untouched for as long as possible.

None of this changes what the numbers mean for you — it's here for anyone who wants to actually trust the machinery, not just the output.

The very first thing you'll see is a choice: Quick & Simple or Full Control. This isn't permanent — a "Change" button stays visible near the top of the page the whole time, so you can switch back and forth freely with no penalty either way.

Quick & Simple shows only Quick Start (below) and hides the more detailed sections of the tool — Build Your Portfolio, Saved Portfolios, the full Retirement Monte Carlo inputs, Historical Stress Test, and Sequence of Returns Risk, plus the Roth Conversion tab disappears from the top navigation entirely. Nothing is deleted or lost — those sections and that tab are simply out of the way until you choose Full Control.

Full Control shows everything — your real fund lineup, state tax, Social Security timing, Roth conversions, other accounts, and every other detail this tool models. If you started in Quick & Simple and later click "Open the Full Tool" from your results, this switch happens automatically and your Quick Start numbers carry over into the matching fields, so you're not starting from scratch.

A 3-step guided version of this same tool, built for getting a real answer in under 2 minutes without needing your actual fund details on hand yet.

• Step 1 — Investment Mix. A slider spanning the full stock/bond spectrum, from 100% Stock to 100% Bonds in 10% increments — slide to whatever's closest to your real mix, with the ratio and its expected return updating live as you move it. That expected return is pulled live from this tool's own current capital market assumptions — the same numbers driving every other calculation here, not a separate simplified guess.

• Step 2 — Your Numbers. Six fields: your age, retirement age, current balance, annual contribution, Social Security benefit and claim age (defaults to match your retirement age, but is fully editable if you plan to claim at a different time), and your annual spending goal.

• Step 3 — Your Projection. The exact same 2,000-path Monte Carlo engine, exact same result panel — gauge, Bad Luck/Median/Good Luck cards, the balance-over-time chart — as the full tool, just built from your Quick Start answers instead of a detailed manual setup. A disclaimer explains what's simplified: no state tax, standard Medicare costs, no other accounts, using your chosen mix's assumptions rather than your real specific fund lineup.

You can save a Quick Start result the same way as any other plan — Saved Scenarios (see below) works from here too, and correctly remembers which investment mix you picked so loading it back brings you right back to where you left off, run button included.

This is genuinely the same tool, not a separate simplified calculator — everything computed here can be refined further any time by switching to Full Control.

1. Add your funds. In "01 · Build Your Portfolio," type in each fund you hold — ticker, name, category, and expense ratio — and click "Add Fund to Your Portfolio." Even if you only know the category (like "Large Blend" or "Real Estate"), that's enough to add it.

2. Set each fund's allocation %. Every fund you add shows up in the table with an editable Allocation % box. The total is hard-capped at 100% — trying to enter more than the room left simply clamps to what's actually available, so you'll never end up over.

3. Set your Account Tax Treatment. Right below your fund table — Pre-Tax, Roth, or Taxable Brokerage. This matters a lot, and it's also what gets remembered if you save this as a Saved Portfolio.

4. Fill in "02 · Retirement Monte Carlo." At minimum, enter your Current Age, Retirement Age, Current Balance, Social Security claim age and monthly benefit amount, and Target Annual Income. These fields start empty with grey example text (like "e.g. 600000") showing the kind of number expected — that's a placeholder, not a real default, so type in your own actual numbers before running anything.

5. Click "Run 2,000-Path Monte Carlo." This is the big gold button. It runs your plan through 2,000 different simulated versions of the future and tells you how many of them worked out.

6. Read the Success Rate. This is the single most important number in the whole tool — the % of simulations where you never ran out of money. Above 85% is generally considered solid; below 65% means real changes are worth considering.

7. Try changing things. Add or remove a fund, adjust an allocation, or change your retirement age, spending target, or Social Security claim age, and run it again. The whole point of this tool is comparing different choices.

This tool doesn't come pre-loaded with any funds — you build your entire portfolio yourself, one fund at a time, right here. There are no tabs to navigate for this part; adding a fund and setting its allocation both happen in the same place.

Adding a fund: type in a ticker (or leave it blank if you only know the category — a placeholder name gets generated), a display name, its category, and its expense ratio. The ticker and name are for your own tracking only — the category is what actually drives the return/risk math. The "Look Up on Yahoo Finance" button opens that ticker's real page in a new tab so you can check its actual numbers yourself. Click "Add Fund to Your Portfolio" and it appears in the table below.

What the table columns mean:

• Exp. Ratio — the yearly fee the fund charges you, as a percent of your money. Lower is better.

• Est. Return* and Est. Std Dev* — how much this type of fund is expected to grow per year on average, and how bumpy that ride tends to be. These come from real, current forecasts by major investment firms, not just a guess.

• Est. Sharpe* — a single number combining return and bumpiness into "how much reward am I getting for the risk I'm taking." Higher is better.

• Score — 0 to 100. Combines cost, the Sharpe number above, and how different this fund is from the rest of your portfolio (owning different things that don't move together is usually good — it's called diversification).

• Allocation % — type here to say what % of your money should go in this fund. The total across your whole portfolio is capped at 100% automatically — the bar at the bottom shows your running total.

• Remove — takes the fund out of your portfolio entirely.

A quick way to switch between a few different fund lineups without needing to run anything first — useful if you want to compare "my current 401(k) mix" against "what if I went more aggressive," or maintain a couple of standard mixes you like to test against different retirement plans.

Give it a name and click "Save Current Portfolio" — it remembers your fund list, allocation, and Account Tax Treatment (but not your age, balance, or spending — those live in Saved Scenarios instead, which capture a complete plan including results). Click "Load" on any saved portfolio to swap your current fund table for that one instantly.

This is deliberately simpler than Saved Scenarios below — no simulation results attached, just the building blocks of a portfolio, ready to plug into whatever plan you're currently working on.

This is worth understanding properly, not just as a line in the Score description above — it's one of the more important ideas in this whole tool, and one of the few genuinely useful "free" things in investing.

When you hold things that don't move in perfect lockstep, the ups and downs of the combined portfolio are smaller than the average of the individual ups and downs. Harry Markowitz — who won a Nobel Prize largely for formalizing this — called it "the only free lunch in investing," because it's one of the rare places you can reduce risk without necessarily giving up expected return. Almost every other choice in investing is a real tradeoff; this one, done well, mostly isn't.

This is exactly what the Score column's diversification piece is measuring, live: a fund gets less credit the more it overlaps with what you already hold, and more credit the more it fills a genuine gap. It's also why bonds typically add more diversification value than another stock fund does — in this tool's own correlation numbers, bonds vs. stocks sit around 0.05 (barely related), while different stock regions sit around 0.55–0.75 (related, but not identical — still useful, just less powerful than bonds).

The honest limit: diversification reduces the risk specific to one company, sector, or country. It does not eliminate market-wide risk — the risk that everything falls together in a genuine crisis. And there's a cruel irony here: in a real crisis, correlations tend to rise toward 1 across almost everything, precisely when you'd want diversification protecting you most. 2008 is a good example — a lot of "diversified" portfolios still fell together hard, because that crisis was systemic, not sector-specific. Diversification is real and worth having, but it's not a guarantee against loss, and it's not a substitute for the other levers in this tool — how much you spend, when you retire, how much cash cushion you keep.

What's a "Monte Carlo simulation"? Instead of guessing one single future for the stock market, this tool imagines 2,000 different possible futures — some where markets do great, some where they do badly, most somewhere in between — and checks whether your money lasts in each one. The % that worked out is your Success Rate.

The main fields:

• Current Age / Retirement Age / Plan Until Age — self-explanatory, but note "Plan Until Age" should be an age you might realistically live to (like 90 or 95), not your best guess at your actual lifespan — the risk being tested is outliving your money.

• Your SS Claim Age / Amount — from your real Social Security statement. You can pick any claim age from 62-70; later claiming means a bigger monthly check.

• Target Annual Income — how much you want to spend per year, in today's dollars (what that amount buys you right now). The tool automatically grows this number with inflation for future years — so if you see a much bigger number later in the results, that's not a mistake, it's the same buying power in future dollars.

• Current Balance — your portfolio's balance today. Its tax treatment is set back in "01 · Build Your Portfolio," right after your fund table — Pre-Tax (a Traditional 401(k)/IRA) means ordinary income tax and Required Minimum Distributions apply; Roth means withdrawals are completely tax-free and RMDs never apply; Taxable Brokerage means only the profit portion is taxed, at capital gains rates, and RMDs don't apply either. Worth double-checking that dropdown is set correctly — it changes the tax math throughout the entire tool. If your real money is split across more than one of these treatments, put your main pot there and use "Other Assets & Accounts" below for the rest.

• Tax Filing Status and Born In (Year) — used to calculate your real taxes and the age you're legally required to start withdrawing money (called an RMD — see the Glossary).

Withdrawal Method — three choices for how you take money out each year:

• Target Annual Income — spend the same amount (adjusted for inflation) no matter what the market did. Predictable, but can drain your savings faster in a bad market.

• Withdrawal Rate — spend an exact percentage of your portfolio balance every year. Important: this rate excludes Social Security and any pension entirely — those are added as separate income on top of whatever the portfolio contributes, not folded into the rate. (This is the opposite of Target Annual Income mode, where the number you set already includes Social Security as part of the total.) Your spending automatically shrinks in bad years and grows in good years, which is safer for your money but means your income isn't the same every year.

• Guardrails (Guyton-Klinger) — a real, published strategy that sits between the other two. Spending grows with inflation most years, just like Fixed. But every year, the tool checks your current withdrawal rate (that year's planned spending ÷ that year's balance) against two "guardrails" set around your starting rate. Drift too far above the top guardrail (balance shrinking faster than planned) and spending gets cut by a set amount. Drift too far below the bottom guardrail (balance growing faster than planned) and spending gets raised. Otherwise, nothing changes. See "Guardrails Fields" below for the three numbers that control this.

Override Expected Return — normally off. Turn it on if you want to manually test "what if returns were only X% instead of what the fund table calculated" — useful for stress-testing your own assumptions.

• Initial Withdrawal Rate — your spending in the very first retirement year, as a % of your starting balance. This is also the "home base" rate the guardrails are measured against. 5% is the classic Guyton-Klinger starting point (higher than the more conservative 4% rule, because the guardrails themselves are what make a higher starting rate safe).

• Guardrail Band — how far your current rate can drift from the initial rate before a rule kicks in. The standard value is 20% — with a 5% initial rate, that puts the guardrails at 4% and 6%.

• Spending Adjustment — how big the cut or raise is when a guardrail is hit. The standard value is 10%. A quiet detail worth knowing: the tool also skips your inflation raise entirely in any year right after a year the market lost money — a real part of the original Guyton-Klinger method, not something you can turn off separately.

Hidden by default to keep things simple. Turn it on if you're married and want this plan to account for any of the following: your spouse's own Social Security benefit, your spouse working and retiring on a different schedule than you, or what happens financially if your spouse passes away before you do.

• Spouse Age Gap — how many years older or younger your spouse is. This matters because your spouse's own retirement and Social Security timing depend on their age, not yours.

• Your Age When Spouse Predeceases You — a hard thing to think about, but important: when one spouse passes away, the survivor's taxes often go up (smaller deduction, higher rates) while their spending needs barely drop. This box lets you see that risk honestly instead of ignoring it.

• Spouse's Own Pre-Tax Retirement Balance — if your spouse has their own separate 401(k) or Traditional IRA, put it here, not in "Current Balance" above (which is yours). This matters because RMDs are based on each person's own birth year — if you lumped your spouse's balance into your own portfolio, the tool would use your RMD age for their money, which is wrong whenever there's any real age gap between you. Once your spouse reaches their own RMD age, their required withdrawal shows up as "Spouse's own RMD" in the year-by-year table — it's fully taxable, and it also reduces how much you need to pull from your own portfolio, same as pension income.

• Select Your State — pick your state and a real, current estimated tax rate on retirement income fills in automatically, including the 13 states that don't tax retirement income at all. Graduated-tax states (like California or New York) show a single representative rate, not a full bracket calculation — choose "Other / Enter Manually" if you know your actual rate more precisely.

• Medical Inflation Rate — healthcare costs usually rise faster than everything else, so this has its own, separate (usually higher) growth rate.

• Pre-65 Healthcare Bridge Cost — if you retire before 65, Medicare isn't available yet, so you'd need to buy your own health insurance. Type in your own estimate of what that costs per year — the tool doesn't look this up or calculate it for you, and it treats it as a flat yearly amount that grows with Medical Inflation. A real insurance quote (or last year's premium, if you already have coverage lined up) will be more accurate than a guess — actual marketplace premiums also change with your income, which this simple estimate doesn't account for.

• One-Time Event — a single inheritance, home sale, or big one-time expense at a specific age. Positive number = money coming in; negative = money going out.

A "Roth conversion" means deliberately moving money from your regular 401(k) into a Roth account earlier than you have to. You pay tax on it now — but after that, it grows completely tax-free forever and you're never forced to withdraw it. Many people do this in the early retirement years, after they stop working (lower income = lower tax bracket) but before required withdrawals start in their 70s.

This section on the main page is just a quick status card — "Currently on/off" plus a summary of your settings. The actual toggle, conversion amount, age range, the Break-Even Tax Rate calculator, and a tool for comparing several conversion amounts side by side (including $0, so "not converting" is always one of the options being compared) all live on their own dedicated Roth Conversion tab in the top navigation. Whatever you set there carries over automatically — click "Run 2,000-Path Monte Carlo" back on the Analyzer tab afterward to see the full effect on your Success Rate.

This whole tab only appears in Full Control mode — it's genuinely advanced territory (its own calculator, its own comparison tool), so it's one of the things hidden while in Quick & Simple. If your main account isn't Pre-Tax, a clear warning appears right at the top of this tab explaining that conversions won't do anything in that case, since there's nothing pre-tax to convert from.

Appears next to the legend once you've allocated money to at least one fund, in "01 · Build Your Portfolio." Shows your current allocation broken down by the same five asset-class groups used throughout this tool — Bonds, US Equity, Foreign Developed, Emerging Markets, and Alternatives — computed the same way as the diversification part of the Score column, and updates live as you adjust allocations.

The conventional rule of thumb — "convert if you expect a higher tax rate later" — is a reasonable starting point, but it understates when converting actually makes sense. This calculator answers a sharper question: at exactly what future tax rate does converting stop mattering — where converting and not converting produce the identical dollar result?

If you genuinely expect to face a higher rate than that break-even number when you'd actually withdraw the money, converting looks favorable. If lower, it may not pay off — even if you still expect some future rate increase.

One specific, honest note: this tool's break-even rate comes out lower than your current marginal rate, not equal to it. That's not a mistake — it reflects how this specific tool actually executes a conversion: the full amount you specify moves into the Roth, and the resulting tax bill is paid by pulling extra from what's left in the Traditional side, rather than shrinking the converted amount itself. That's more favorable to converting than the simplest textbook comparison — where the money to pay conversion taxes comes from genuinely changes the real answer.

Two ways to fill in the current rate and growth rate fields — neither one is "more real" than the other, they're just different sources for the same two numbers. Fill in Target Annual Income and build your portfolio allocation on the Analyzer tab, and both auto-fill and stay in sync with those — internally consistent with the rest of your plan, but only as accurate as two simplifications: your spending target standing in for that year's actual taxable income, and today's portfolio blend standing in for decades of real returns. Or type your own numbers in directly — genuinely just as accurate, sometimes more so, if you actually know your real tax bracket and have your own return assumption — but this tool has no way to check a manual entry against the rest of your plan, so if it drifts from what the Analyzer tab would imply, this result and the main simulation could tell two different stories. The result box tells you which case currently applies.

This is a standalone, simplified estimate either way — flat assumed rates, not the full year-by-year bracket, RMD, and IRMAA interaction the main simulation above already models for your actual plan. Use it as a sanity check on the conversion amount and timing you've set, not a replacement for comparing Success Rate with the strategy on versus off.

Hidden by default. Turn it on if your 401(k) isn't your only money — most people also have some cash savings, maybe a brokerage account, maybe an IRA, maybe an existing Roth.

Why this matters: having other money changes how much your 401(k) needs to do. This section spends your money in a specific, deliberate order every year: Social Security first, then cash (it's free — no tax to use it), then your brokerage account (only the profit portion gets taxed, usually at a lower rate than regular income), then your 401(k)/Traditional IRA, and finally Roth money as a last resort — kept for last because it's the most valuable dollar-for-dollar (completely tax-free), so it's worth leaving alone as long as possible.

• Cash / Savings Balance — checking, savings, CDs. Held completely flat (0% growth) by default, since real bank cash doesn't grow like an invested portfolio — that's the honest, conservative assumption. If this money is actually in a high-yield savings account or CD, an optional Assumed Cash Yield field next to it lets you model a real, fixed annual rate instead.

• Traditional IRA Balance — taxed exactly like your 401(k), so it's simply combined with it behind the scenes.

• Taxable Brokerage Balance and Cost Basis % — a regular investment account. "Cost basis" means how much of it is your original money versus growth — only the growth portion gets taxed when you sell. If you're not sure, 50% is a reasonable guess for an account you've held a long time.

• Existing Roth Balance — any Roth IRA or Roth 401(k) you already have. Unlike before, this tool now actually spends from your Roth if everything else runs out, instead of just showing it as leftover money at the end.

• Brokerage Risk Type and Roth Risk Type — by default, both of these accounts grow at the exact same simulated return as your main portfolio every year, which is a simplification: a real Roth or brokerage account could easily be allocated completely differently (many people invest their Roth more aggressively, for instance). Pick a risk type — 100% Stock down to 100% Bonds or Money Market — to give either account its own independently-simulated, realistic return and volatility instead, derived from the same current capital market assumptions as everything else in this tool. Or, if you have a specific return number in mind, the paired Override Return field locks that account to a fixed, non-random rate every year instead — takes priority over the risk type if both are filled in.

Hidden by default — most people today don't have one, but if you or your spouse worked somewhere with a traditional pension (common in government, military, and some union jobs), turn this on.

• Pension Amount and Pension Start Age — your monthly check and when it begins.

• Pension COLA — whether it grows with inflation. Defaults to 0% on purpose: most private-sector pensions do NOT increase over time — the same dollar amount for life, which quietly buys less and less as the years go by. Check your own plan paperwork; government pensions more often do have a real COLA.

Hidden by default. A QCD (Qualified Charitable Distribution) is a real, valuable IRS rule: once you're 70½, you can send money directly from an IRA to a charity, and that money is never counted as taxable income at all — better than withdrawing it, paying tax, and then donating what's left.

Only turn this on if charitable giving is genuinely part of your plan. Set an annual amount, and the tool applies it starting at age 70½, capped at the real 2026 IRS limit ($111,000/person/year) and at whatever balance you actually have.

The main simulation answers "does this spending level work?" — this answers the reverse, more commonly-wanted question: "what's the most I can safely spend?" Pick a target success rate (85% is a common default), click "Find My Safe Spending Level," and it searches for the highest spending your exact plan can sustain at that success rate — same age, balance, allocation, and everything else exactly as configured above.

In Target Annual Income mode, this finds a dollar amount per year. In Withdrawal Rate or Guardrails mode, it finds the withdrawal rate itself, since those methods are already percentage-of-balance based.

One honest limitation: Withdrawal Rate mode's own definition of "success" doesn't meaningfully constrain very high rates — a percent-of-balance withdrawal mathematically shrinks your balance toward zero without ever exactly reaching it, so it rarely counts as a real "failure" even at rates no real retirement should use. If the search hits this, you'll see a note explaining it rather than a misleading number — switch to Target Annual Income mode for a more concrete answer in that case.

Appears after you click "Run 2,000-Path Monte Carlo." Here's what each card means:

• Success Rate gauge — the same headline number as a speedometer-style dial, color-coded the same way as everywhere else in this tool (teal ≥85%, gold 65–84%, red below that), for a quicker visual read before you look at the exact percentage.

• Success Rate — the % of the 2,000 simulated futures where your money never hit $0. The headline number.

• Bad Luck / Median / Good Luck balances — three snapshots of your ending balance: a pessimistic (but realistic) case, a typical case, and an optimistic case. These give you a range instead of one falsely-precise number.

• Traditional vs. Roth breakdown — appears automatically if you turned on Roth Conversion Strategy or added an existing Roth balance under Other Assets, showing the Bad Luck/Median/Good Luck split between your Traditional and Roth balances side by side. If your 401(k) money runs out, Roth is also now spent as a last resort, so it's not just leftover money.

• Max Drawdown — the worst drop your balance takes at any point before recovering, among the simulations that succeeded. A 60% drawdown means your balance was cut more than in half at its worst moment, even in a scenario that ultimately worked out.

Below the cards is a chart showing your balance over time across the three scenarios — hover anywhere on it (or drag a finger on mobile) to see the exact age and all three percentile balances at that point — and a written summary explaining what the numbers mean for your specific plan.

The written summary above tells you that your plan has a certain Success Rate and gives general advice ("consider trimming spending, working slightly longer"). This button answers the sharper, more useful question: which specific change actually helps the most, and by how many points?

Click it and the tool tests up to five realistic single changes against your exact current plan — delaying retirement by 2 years, reducing your spending goal by 10%, increasing your annual contribution by 25%, shifting roughly 20% of your portfolio toward bonds, and delaying Social Security to age 70 — each one its own full 2,000-path simulation, so this takes about 10-15 seconds. A final row shows what stacking the two most helpful changes together would do. Nothing about your actual plan changes from clicking this — every field and your portfolio's return/risk are restored to exactly what they were once the results are shown.

Results are rounded to the nearest 5 percentage points, since two runs of the exact same plan can differ by a couple of points from simulation randomness alone — a difference smaller than that isn't a real effect worth acting on. And it's worth reading honestly: not every change helps. Delaying Social Security, for instance, can genuinely hurt a plan that needs the portfolio to cover more spending in the years before that larger check arrives — the diagnostic will show that as a negative number when it's true, not just report good news.

A detailed, age-by-age breakdown. Three tabs above it — Bad Luck / Median / Good Luck — let you see the same table under each scenario.

• Balance — how much you have at the end of that year.

• Social Security — your benefit that year (grows a little each year, like real Social Security does).

• Portfolio Withdrawal — how much you pulled from your 401(k) that year, before tax. Notes underneath explain anything unusual happening that year (a required withdrawal, an early-withdrawal penalty, Medicare costs, etc.).

• Std. Deduction, Total Tax, Eff. Tax Rate — your real, calculated taxes for that year, not a guess.

• Spendable Income — what you actually get to live on that year, after tax. Also shows the same amount converted back to "today's dollars" so you can tell if it's really more money or just a bigger-looking number due to inflation.

A Total row at the bottom adds everything up across all the years shown.

The Monte Carlo above uses randomly generated market years. This section instead uses the real stock and bond returns that actually happened, every year from 1995 to 2024 — including the real 2008 financial crisis, the real 2020 COVID crash, and the real 2022 downturn.

Click "Run Historical Backtest" and it replays your plan starting from each of those 30 real years, showing whether your money would have survived and how bad the worst dip got, using what genuinely happened rather than a computer-generated guess.

Three highlighted cards show exactly what would have happened if you'd retired right at the start of 2008, 2020, or 2022 — the three toughest recent starting points to retire into.

This is one of the most important, least intuitive ideas in retirement planning: the order your returns arrive in matters just as much as their average. Two people can retire with identical portfolios, identical spending, and experience the exact same average return over 30 years — and end up in completely different places, purely based on whether the bad years hit early or late.

Click "Show Sequence of Returns Risk" and it takes the real 1995–2024 market data already used in the Historical Stress Test and runs your exact plan through it twice: once in the order it actually happened, and once with that same set of returns reversed. The average annual return is mathematically identical between the two — reversing the order of a list never changes its average — so any difference in outcome comes purely from timing, not from one sequence being "better" than the other.

Why order matters: a bad year that hits while your balance is large and you're actively withdrawing forces you to sell more shares while prices are down, and that loss compounds for the rest of retirement. The same bad year hitting decades later, after good years have already grown your balance, does far less damage. This is why retiring even a few years earlier or later than a friend, with an otherwise identical plan, can lead to a very different outcome — it isn't always about being a better investor, sometimes it's just when you happened to retire.

Lets you compare different plans side by side instead of overwriting your results every time you run something new. After running a projection — from Quick Start or the full Monte Carlo — give it a name and click "Save Current Scenario" — it captures your current results, your full inputs, and every toggle. Change something (a later retirement age, a different allocation, a Roth conversion strategy) and save again under a new name; the comparison table lets you see every saved scenario's Success Rate and balances at a glance.

The "Method / Mix" column shows whichever is actually meaningful for how that scenario was built: your Withdrawal Method for a Full Control scenario, or your chosen Investment Mix for a Quick Start one — a single table can hold a mix of both kinds side by side.

Each row also has a "Load" button, which restores every input from that exact scenario back into the tool — including switching back to whichever mode (Quick & Simple or Full Control) it was actually saved from, and landing you back on the right step if it was a Quick Start scenario. Saved Scenarios are included automatically in Export Full Plan and this tool's browser auto-save, so they survive both a page reload and an export/import round trip.

This tool auto-saves your work to this browser as you type — the indicator near the top shows the last save time, and reloading the page offers to restore it. That's local to this device and browser only, not sent anywhere, so it's worth knowing about the other options too:

• Export Portfolio (CSV) — just your fund list (ticker, category, allocation, expense ratio, score) as a spreadsheet file.

• Export Full Plan — a genuine complete backup: every fund, every setting, every toggle, every Saved Scenario, and every Saved Portfolio. Use this before switching devices or browsers, or just to keep an external copy.

• Import Plan — loads a previously-exported JSON file back in, replacing everything currently in the tool after you confirm, including switching to whichever mode (Quick & Simple or Full Control) that file was actually saved from. This is the way to move a plan to a different device, or restore an older version of your work.

• Clear saved data and Start Fresh are two different things, worth not confusing: "Clear saved data" only affects what gets offered back to you next time you open this page — your current on-screen work is untouched. "Start Fresh" is the real reset: every field, every Saved Scenario, every Saved Portfolio, and your mode choice, all permanently erased, reloading the page exactly as it looked the first time you ever opened it. Export first if there's anything in either you'd want to keep.

Q: Why does my spending target show as a much bigger number later in the tables?
Because of inflation. If you retire in 8 years, $60,000 today needs to become roughly $76,000 in 8-years-from-now dollars just to buy the same amount of stuff. The tool automatically grows your target so your real buying power stays the same — it's not spending more, it just looks bigger in future dollars.

Q: Why is my "Portfolio Withdrawal" higher than my spending target minus Social Security?
Because that withdrawal is before tax, and it also has to cover your Medicare premiums. The tool automatically pulls out a bit extra to cover taxes and healthcare costs so that what's actually left over matches your real spending target.

Q: I set my Withdrawal Rate to 4% — shouldn't my withdrawal always be exactly 4% of my balance?
Yes, and it is — 4% of your balance right before that year's withdrawal comes out (not the balance shown afterward in the table, which is already reduced by that withdrawal). The two numbers look different because they're two snapshots of the same year.

Q: Why don't I see my employer's actual plan funds pre-loaded?
This tool doesn't pre-load any funds — everything starts empty, and you build your portfolio entirely by adding funds yourself in "01 · Build Your Portfolio." That keeps things simple and puts you in full control of exactly what's in your plan, including funds outside your employer's list.

Q: Should "RMD floor" show up in the table if my money isn't actually in a 401(k) or IRA?
No — and it won't, as long as you enter things in the right place. RMDs (Required Minimum Distributions) are a real IRS rule that applies only to pre-tax retirement accounts (a Traditional 401(k) or Traditional IRA) — never to a Roth account or a regular taxable brokerage account. The "Current Balance" field in section 02 is always treated as that pre-tax account, so it's always subject to RMDs once you reach RMD age. If some of your money is actually in a Roth or a taxable brokerage account, don't put it in "Current Balance" — enter it under "Other Assets & Accounts" instead, where it correctly gets the right tax treatment and is correctly left out of the RMD calculation.

Q: I added a fund that holds both US and international stocks (like a "World Stock" fund). How does the tool score it and factor it into my portfolio's risk?
Most fund categories are one pure asset class — all US, all bonds, all emerging markets — so the tool can cleanly say "this fund behaves like US stocks" or "this fund behaves like bonds." A world/global stock fund genuinely doesn't fit that: it's really two things blended into one fund. So instead of forcing it into a single bucket, three specific categories are modeled as an actual mix and get the credit that mix deserves everywhere it matters:

• "World Large Stock (Global Blend)" — treated as 60% US / 40% international

• "Global Real Estate" — treated as 35% US / 65% international

• "Balanced / Allocation (60/40)" — treated as 60% stock / 40% bond

This split shows up in three places: the Score column gives the fund partial diversification credit — not full credit (since part of it overlaps with US holdings you may already have), and not zero credit either. Your portfolio's overall volatility (the "Weighted Std Dev" number) reflects the real risk-reducing benefit of the international portion, which you can actually see: adding a 50/50 mix of a pure-US fund and a World Stock fund lowers your portfolio's estimated volatility more than a same-size all-US portfolio would, because the two halves don't move in perfect lockstep. And in the Historical Stress Test, a Balanced (60/40) fund correctly counts as 60% stock-like and 40% bond-like when picking which real historical returns to apply, instead of being treated as 100% stock. Every other category is still one pure asset class, which is accurate for the large majority of real funds — this blending only applies to the few categories named above.

Q: In the Historical Stress Test, "Starting Year 2008" shows a huge ending balance. Wasn't 2008 a crash? Where does that number come from?
"Starting Year" does NOT mean "the year I retire" — it means the year the real market history starts being applied, which is today in the simulation, not your retirement date. If you're 57 now and plan to retire at 65, "Starting Year 2008" means: the 2008 crash happens while you're 58 and still 7 years away from retirement, still working and still contributing money every year. A crash while you're still buying is actually good for you long-term — you're picking up shares at low prices, and then you get to ride the recovery years (2009-2014 were very strong) before you ever touch the money at retirement. This is a real, well-known idea in investing called "sequence of returns" — a crash early in your saving years barely hurts you; a crash early in your spending years is what's actually dangerous, because you're forced to sell investments at low prices to cover expenses. If you want to see the truly risky version — a crash landing exactly when you retire — temporarily set "Current Age" equal to "Retirement Age" before running the backtest, so there's no gap between today and retirement.

Q: Is this tool giving me real financial advice?
No. It's an educational and planning tool built to help you understand your own numbers and explore "what if" scenarios. It is not a substitute for a licensed financial advisor or a CPA, especially for a decision this important.

Monte Carlo simulation — running thousands of randomly-generated possible futures to see how often your plan works out, instead of relying on one guess.

RMD (Required Minimum Distribution) — the IRS forces you to start withdrawing a minimum amount from your 401(k) starting at a certain age (73 or 75, depending on your birth year), whether you need the money or not.

IRMAA — an extra charge added to your Medicare premium if your income is above certain thresholds. Higher income in retirement can mean a bigger Medicare bill.

Roth conversion — moving money from a regular (taxable-later) retirement account into a Roth (tax-free-later) account, paying the tax now instead of later.

Drawdown — how far your balance drops from its highest point before it recovers. A 40% drawdown means it fell 40% below its peak at some point.

Expense ratio — the annual fee a fund charges, as a percentage of your investment. A 0.50% expense ratio costs you $50/year for every $10,000 invested.

Standard deduction — an amount of income the IRS lets you earn completely tax-free every year, before any tax rate applies.

Marginal vs. effective tax rate — your marginal rate is what you pay on your next dollar of income; your effective rate is your total tax divided by your total income. The effective rate is almost always lower and is the more honest picture of your real tax burden.

Sequence of returns risk — the danger that a market crash happens right when you start withdrawing money, which does far more damage than the same crash happening later, because you're selling investments at low prices to fund your spending.