Why tax-blind calculators miss by years.
Open ten free FIRE calculators and most run the same loop: annual spending × 25, a growth rate, a date. Taxes appear nowhere — or as a single slider you're supposed to set by feel. Both defaults are wrong, in opposite directions, and both can be wrong by years rather than months.
Skip taxes entirely and every withdrawn dollar is assumed to reach your grocery store intact. For someone whose savings sit mostly in a traditional 401(k) or IRA, it won't: those withdrawals are ordinary income, taxed like a paycheck. Later, required minimum distributions — the IRS's mandatory withdrawals starting at age 73 — stack on top of Social Security whether you need the money or not. A tax-blind calculator quietly tells that saver they can retire earlier than they safely can.
The common fix — assume a flat 15% on everything — fails the other way. Federal tax isn't a flat rate; it's a staircase, and in early retirement most people stand on the bottom steps. A flat 15% can tell a couple living from a taxable brokerage account to keep working years after they were actually done. In fairness, the flat guess has one virtue: it's conservative. If you refuse to do bracket math, it's a safer error than assuming zero. But you don't have to refuse.
The same numbers, walked through the brackets.
Meet a married couple, both 52, who spend $60,000 a year. Their portfolio sits in a taxable brokerage account where about half of any withdrawal is their own original cost basis — money they already paid tax on — and half is long-term capital gain. Run them through three calculators:
| Method | Assumed federal tax | Gross withdrawal needed | FIRE number (25×) |
|---|---|---|---|
| Tax-blind (most free calculators) | $0 | $60,000 | $1,500,000 |
| Flat 15% guess | $10,588 / yr | $70,588 | $1,764,700 |
| Bracket math (what a real engine does) | ≈ $0 — 0% long-term gains bracket | $60,000 | $1,500,000 |
Static on purpose — the interactive version ships with the planner, where the same engine runs your own numbers live. Rounded 2026 federal figures, married filing jointly, as of July 2026.
The bracket math, spelled out: withdrawing $60,000 realizes about $30,000 of long-term gains — the basis half was never taxable to begin with. With no paycheck, the couple's 2026 standard deduction (about $32,200 filing jointly) more than covers it. Taxable income: $0. Federal tax: $0. Even without the deduction they'd owe nothing, because long-term gains "stack" on top of ordinary income and stay at a 0% federal rate until total taxable income passes roughly $98,900. In practice, a couple with no wages can realize around $131,000 of long-term gains a year at 0% federal (figures as of July 2026 — and most states still take their cut, which is why per-state math matters).
For this couple, the flat-15% guess demands an extra $265,000 of portfolio — roughly two to four additional working years, depending on savings rate — to pay a tax bill that doesn't exist.
Now the honest flip. Give the same couple the same $60,000 from a traditional IRA instead. Every dollar is ordinary income; after the standard deduction, about $27,800 climbs the 10% and 12% steps and the bill comes to roughly $2,800 — an effective rate under 5%. Still nowhere near 15%, but no longer zero, and it grows: by 73, required distributions and Social Security pile onto the same staircase, and the withdrawal order chosen in your 60s decides how hard. The point isn't that taxes are always small. It's that where your money lives changes the answer by tens of thousands of dollars — and a slider can't know that.
What "includes taxes" has to actually mean.
"Does taxes" can mean a marketing checkbox or a statute. Foundera's planner carries a statutory US tax engine — the actual rules, not an average: federal brackets, long-term capital-gains stacking, FICA while you're still earning, AMT, NIIT, QBI, the formula that decides how much of your Social Security is taxable, and per-state income tax. Every year of a projection to age 90+ effectively files its own small tax return. On the Plus tier, Monte Carlo analysis then stress-tests the plan against a thousand simulated market histories, because the sequence of returns matters as much as the average.
If you're comparing dedicated planners: ProjectionLab is the strongest name in this space and takes taxes seriously too — we wrote an honest side-by-side at Foundera vs ProjectionLab. The structural difference is what feeds the plan: assumptions you typed once, or the spending you actually do. That second half is its own story — see why your budget and retirement plan should talk.
Run your brackets, not ours.
The table above is one couple. Your basis, your state, your account mix will land somewhere else — which is the whole point. The planner is free to start, works fully offline, and doesn't ask for an account or an email: your plan is a file on your device. Bring spending in by CSV today; live bank sync via Plaid is coming soon on the Plus tier, and we won't pretend otherwise until it ships.
Open the planner — no account needed →Questions people actually ask.
Do FIRE calculators include taxes?
Most free ones don't — they project spending × 25 and leave taxes to you. A few offer a single flat-rate field, which is better than nothing but still misses bracket effects, capital-gains stacking, and state tax. A true FIRE calculator with taxes computes each year's bill from the statutes.
What tax rate should I assume for early retirement?
Ideally, none — assume a computation instead. Couples funding life from a taxable brokerage often land at 0–5% effective federal; heavy pre-tax savers start low and climb once RMDs and Social Security arrive after 73. Any single assumed rate is wrong for at least one stretch of your retirement.
What is capital-gains stacking?
Ordinary income (wages, IRA withdrawals, interest) fills the tax staircase first. Long-term capital gains then stack on top and use their own gentler schedule — 0%, 15%, or 20% — based on where they land in total taxable income. That's how a no-wage couple can realize six figures of gains at 0% federal, as of July 2026.
Is the 4% rule before or after taxes?
Before. The withdrawal has to cover both your spending and the tax on the withdrawal itself. If taxes run $5,000 a year, your "spending" for the 25× rule is really spending + $5,000 — which is why getting the tax number right moves the whole target.