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Fat FIRE Calculator

Enter your target annual spending, safe withdrawal rate and savings plan to see your Fat FIRE number and timeline.

How it is calculated

The target is FIRE number = annual_spend ÷ (withdrawal_rate ÷ 100), and the gap is max(0, target − current_portfolio). The years needed assume yearly compounding with savings added at the end of each year: with g = annual_return ÷ 100, years = ln((target × g + savings) ÷ (portfolio × g + savings)) ÷ ln(1 + g). With a zero return it is gap ÷ savings. If you already have the target, years show 0.0. If the target can never be reached (for example no savings and no return, or no savings with a portfolio of zero), the years field shows Never. The monthly spend is annual_spend ÷ 12. Spending and withdrawal rate must be above zero, and the withdrawal rate cannot exceed 100; portfolio, savings and return cannot be negative. Otherwise no result is shown. The return is a fixed nominal rate, and savings do not rise with inflation or pay.

Worked example

You want to spend 150,000 a year, use a 3.25% withdrawal rate, hold 1,200,000, save 120,000 a year and expect 6% a year. FIRE number: 150,000 ÷ 0.0325 = $4,615,384.62. Gap: 4,615,384.62 − 1,200,000 = $3,415,384.62. Years: ln((4,615,384.62 × 0.06 + 120,000) ÷ (1,200,000 × 0.06 + 120,000)) ÷ ln(1.06) = ln(2.067) ÷ 0.0583, which is 12.5 years. Monthly spend: 150,000 ÷ 12 = $12,500.00.

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Common mistakes

  • Using the standard 4% withdrawal rate for a very long retirement. A lower rate such as 3.25% raises the target sharply; 150,000 at 4% would be 3,750,000, almost a million less.
  • Entering after-tax spending when the portfolio is tax-deferred. The withdrawals must cover the tax too, so use the gross amount you need to take out.
  • Counting your home's value in the current portfolio. Only investable assets that will fund spending belong there.
  • Entering an optimistic return. A 9% return in place of 6% shortens the timeline a lot, so also check with a cautious rate.
  • Entering savings as a percentage of income. The field takes a money amount per year. If you enter 0 for savings and 0 for return, the tool shows Never, while 0.0 years means you already have the target.

Sources

About this calculator

Fat FIRE is a variant of the Financial Independence, Retire Early movement aimed at retiring without cutting your lifestyle — typically targeting $100,000 or more in annual spending, well above the lean or “barista FIRE” tracks. Because a fatter lifestyle means a much larger portfolio is needed, and because a longer time horizon carries more sequence-of-returns risk, Fat FIRE planners often use a more conservative safe withdrawal rate of around 3–3.5% instead of the standard 4%, so the target portfolio is your annual spending divided by that lower rate.

Reaching that number is then a function of how much you save each year, your expected investment return, and how long you let compounding work — the same mechanics as any FIRE calculation, just aimed at a bigger target.

Your target annual spending, safe withdrawal rate, and savings plan go in; out come both your Fat FIRE number and the estimated years to reach it.

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