About this calculator
This calculator is for education only and does not constitute investment advice. FIRE — financial independence, retire early — has one famous shortcut: save 25 times what you spend in a year, and a 4% annual withdrawal covers that spending indefinitely in the historical simulations behind the rule.
This page runs that shortcut honestly: it solves for the years your savings rate and return need, then keeps simulating through retirement, so you see whether the money actually lasts the withdrawal period — and what happens if it does not. Spending is held flat in nominal dollars; if your spending rises with inflation, the target rises with it.
How to use it
- Enter annual income and the savings rate — the calculator derives annual savings from them.
- Enter the annual spending retirement must fund; the FIRE number is 25 times that figure.
- Enter the assumed return and any savings you already have.
- Read the years to FIRE, then scan the table: accumulation rows build the balance, withdrawal rows spend it down.
The formula
The 25× target is the inverse of a 4% withdrawal rate: withdrawing 4% of the target each year reproduces exactly the annual spending figure. Accumulation adds each year's savings at year end after that year's return, which is why the closed-form balance uses the annuity factor ((1+r)ᵗ − 1)/r. The withdrawal phase applies the same return first, then subtracts spending at year end. The model uses one constant return and flat spending throughout — real returns vary, real spending usually rises with inflation, and taxes are not modeled.
Worked example
Income $100,000, spending $40,000, savings rate 50% ($50,000 a year), return 7%, no current savings: the FIRE number is $1,000,000 and the math gives 12.94 years, so 13 years of saving — the balance after year 13 is $1,007,032.14. Spending $40,000 a year for 30 years after that still leaves $3,887,354.06, because 7% growth on a seven-figure balance outruns a $40,000 withdrawal; at a lower return the same plan can run out, which the table will show.
Sources: 25× target from the 4% safe-withdrawal rule (Trinity study lineage); accumulation and withdrawal simulated year by year at a constant assumed return. Nominal figures — spending is held flat, not inflation-adjusted. Last updated: October 2026.
Frequently asked questions
Where does 25× come from?
From the 4% rule: 1 / 0.04 = 25. The rule comes from historical US market simulations (the Trinity study lineage) in which withdrawing 4% of the starting balance, adjusted for inflation, survived 30-year retirements in most historical windows. It is a planning rule of thumb, not a guarantee.
Why does the withdrawal balance grow in the example?
Because 7% of $1,000,000 is $70,000 — more than the $40,000 withdrawn. The plan is over-funded at that return. Cut the return to 3% and the same 30 years of withdrawals end far lower; the table lets you see that crossover directly.
Does this adjust spending for inflation?
No — spending is held flat in nominal dollars, which flatters the plan. If you expect spending to rise about 3% a year, enter a correspondingly higher spending figure, or treat the result as a lower bound on the target.
Are taxes included?
No. The model is pre-tax: real withdrawals from tax-deferred accounts owe income tax, and taxable accounts owe tax on gains and dividends. A real plan needs a tax line the calculator deliberately leaves out rather than guessing.
What formula does this fire calculator use?
FIRE number = annual spending × 25; balance(t) = current × (1+r)ᵗ + savings × (((1+r)ᵗ − 1) / r); withdrawal year: end = start × (1+r) − spending The 25× target is the inverse of a 4% withdrawal rate: withdrawing 4% of the target each year reproduces exactly the annual spending figure. Accumulation adds each year's savings at year end after that year's return, which is why the closed-form balance uses the annuity factor ((1+r)ᵗ − 1)/r. The withdrawal phase applies the same return first, then subtracts spending at year end. The model uses one constant return and flat spending throughout — real returns vary, real spending usually rises with inflation, and taxes are not modeled. The worked example on this page applies the formula step by step with real numbers, so you can verify the result by hand.