How to use this Fat FIRE calculator
- Pick a tier (Chubby or Fat) or enter your own yearly spending after tax, in today's dollars.
- Enter the effective tax rate you expect on withdrawals (the table below helps you pick one), then your age, investments, take-home pay and yearly savings.
- Check the withdrawal rate under Assumptions. It starts at 3.5%, and the table shows 3% to 4% side by side.
Results update as you type. Copy the share link to save your scenario, or download the year-by-year projection as a CSV.
How do you calculate a Fat FIRE number?
Your Fat FIRE number is the portfolio that funds your spending plus the tax on what you withdraw. It takes four steps:
- Estimate what you'll spend each year after tax, in today's dollars, including health insurance before Medicare.
- Estimate your effective tax rate on withdrawals. The 2026 table further down gives a federal starting point.
- Gross up spending for that tax to get the yearly withdrawal.
- Divide the withdrawal by your withdrawal rate.
As one formula:
Fat FIRE number = spending ÷ (1 − effective tax rate) ÷ withdrawal rate
A 4% rate is the classic 25x rule from William Bengen's research[5]. A 3.5% rate means about 28.6x, and 3% means 33x.
The number leaves out Social Security and pensions, which errs on the safe side for an early retirement. If you want later income to lower it, the FIRE number calculator values each income from the age it starts.
Worked example
Morgan, 40, and their spouse file jointly and want to spend $150,000 a year. To be cautious, they assume every dollar comes from traditional 401(k)s and IRAs, so it is all taxed as ordinary income. They have $1,500,000 invested and save $120,000 a year. The real return is 3.79%.
- Gross withdrawal: $169,667. After the $32,200 standard deduction, 2026 federal tax on it is $19,667, which leaves $150,000 to spend[13].
- Effective tax rate: $19,667 ÷ $169,667 = 11.6%. Entering this rate in the calculator gives the same withdrawal.
- Fat FIRE number: $169,667 ÷ 3.5% = $4,847,619
- Time to get there: about 14.5 years, around age 55
The simple 25x estimate, $150,000 × 25 = $3,750,000, would leave Morgan $1,097,619 short.
What assumptions does the calculator use?
Everything is in today's dollars. The real return comes from the Fisher equation, (1 + return − fees) ÷ (1 + inflation) − 1.
- Return: 7% default with 3% inflation. The S&P 500 returned 10.0% a year from 1928 to 2025[7], while Vanguard's 10-year forecast for US stocks is 4.8%-6.8%[8].
- Withdrawal rate: 3.5% default. Morningstar's 2025 safe starting rate for a 30-year retirement is 3.9%[6], and early retirements last longer than that.
- Tax rate: 15% default. This is your effective rate on everything you withdraw (total tax ÷ total withdrawals), not your top bracket. At $150,000 of spending, 15% sits between the 2026 federal rates for all-pre-tax withdrawals: 17.8% single and 11.6% married filing jointly. Replace it with your own estimate.
What tax rate should I use for Fat FIRE?
Use your expected effective rate: total tax divided by everything you withdraw. As a starting point, the table shows 2026 federal income tax if every dollar you withdraw is ordinary income, as it is from a traditional 401(k) or IRA. It takes the standard deduction ($16,100 single, $32,200 married filing jointly) and the 2026 brackets[13].
| Spending | Single | Married jointly | ||
|---|---|---|---|---|
| Withdraw | Rate | Withdraw | Rate | |
| $80,000 | $91,244 | 12.3% | $85,955 | 6.9% |
| $100,000 | $116,885 | 14.4% | $108,682 | 8.0% |
| $120,000 | $143,071 | 16.1% | $131,409 | 8.7% |
| $150,000 | $182,545 | 17.8% | $169,667 | 11.6% |
| $200,000 | $251,918 | 20.6% | $233,769 | 14.4% |
| $250,000 | $327,899 | 23.8% | $299,300 | 16.5% |
| $300,000 | $404,822 | 25.9% | $365,089 | 17.8% |
Our calculation: gross withdrawal needed to spend each amount, and federal tax ÷ withdrawal, if every dollar is ordinary income. 2026 brackets and standard deduction, today's dollars.
To pick your rate, find your spending and filing status. If nearly all your money is pre-tax, use that rate and add your state's income tax. If part of your spending comes from Roth accounts or from a taxable brokerage account, where you pay tax only on the gains and often at the 0% or 15% long-term rate, your rate will be lower.
The table is a simplification. It covers federal income tax only, at 2026 brackets in today's dollars. It leaves out state and local tax, tax on Social Security benefits, any mix of capital gains, the extra standard deduction at 65 and over, and tax credits.
Why do taxes matter more for Fat FIRE?
US income tax is progressive, so the more you withdraw each year, the higher your effective rate. For a married couple drawing only pre-tax money, the federal rate rises from 8% at $100,000 of spending to 16.5% at $250,000. At $150,000 a year, going from a 15% to a 20% effective rate adds about $315,126 to the number at 3.5%.
The calculator doesn't apply the brackets itself. It applies the single effective rate you enter to every dollar you withdraw, so the result is only as good as that estimate. Your real rate depends on how your money is split between pre-tax, Roth and taxable accounts, your filing status and your state.
Where the money sits matters too. Withdrawals from traditional 401(k)s and IRAs before 59½ usually owe an extra 10% tax unless an exception applies[10], and each Roth conversion has its own 5-year clock[11]. A mix of taxable, Roth and pre-tax money gives you more control over your yearly tax bill.
How much can a tax mix lower your Fat FIRE retirement amount?
A lot, because only the gains on taxable investments are taxed, and often at 0%. Say Morgan's household funds its $150,000 with $60,000 from traditional accounts and the rest by selling taxable investments, 50% of which is long-term gain (our calculation, 2026 federal tax):
- Total withdrawal: $152,840 ($60,000 pre-tax plus $92,840 of sales)
- Federal tax: $2,840, an effective rate of 1.9% instead of 11.6% with all pre-tax money
- Fat FIRE number at 3.5%: $4,366,857 instead of $4,847,619
Why so low? After the standard deduction, only $27,800 of ordinary income is taxable. The gains stack on top of it and stay under the $98,900 line where the 0% long-term rate ends for joint filers[13]. The pre-tax money doesn't escape tax, though. Required minimum distributions generally start at 73[14], so drawing taxable money first can mean bigger taxable withdrawals later. Enter the blended rate you expect over the whole retirement, not the rate of your cheapest year.
Why use a lower withdrawal rate for a fat retirement?
A long retirement is the main reason. A 4% rule with a 50/50 portfolio had about 95% success over 30 years but only about 65% over 60 years[4]. Fat FIRE often starts in your 40s, so the money may need to last 50 years.
Fat FIRE has one advantage: room to cut. Guardrail rules reduce spending about 10% when the withdrawal rate drifts too high[12], and that's easier when part of your budget is travel and extras. In Morgan's case, moving from 3.5% to 3% raises the number from $4,847,619 to $5,655,556.
Fat FIRE vs Chubby FIRE: how much more do you need?
The average US household spent $81,905 in 2025[9], so Chubby FIRE is above-average spending and Fat FIRE is well above it. For a married couple drawing only pre-tax money at 3.5%, Chubby FIRE at $100,000 needs $3,105,195, and Fat FIRE at $150,000 needs $4,847,619 after 2026 federal tax (our calculation).
That is 56% more portfolio for 50% more spending, for single people too, because every extra dollar is withdrawn at a higher bracket. Moving from Chubby to Fat FIRE costs more than the budget gap suggests, and a tax mix narrows it.
These dollar tiers are rough community conventions, not official definitions; Fat FIRE simply means a retirement with costly extras like frequent travel[2]. To learn more, read what Fat FIRE is and how it compares.
Fat FIRE vs other types of FIRE
| Type | Annual spending | What it means |
|---|---|---|
| Lean FIRE | Under about $40,000 | Very frugal budget, often in a low-cost area |
| FIRE | About $40,000-$80,000 | Portfolio covers a typical lifestyle |
| Chubby FIRE | About $80,000-$120,000 | Comfortable, some luxuries |
| Fat FIRE | $120,000+ | No meaningful budget constraints |
| Coast FIRE | Any | Saved enough to stop investing; work covers current bills |
| Barista FIRE | Any | Part-time income covers part of spending |
Spending bands are this site's rough conventions, not official definitions; they shift with inflation and cost of living.