Your FIRE number is the portfolio that can pay your bills for good: annual expenses divided by your safe withdrawal rate. Add what you have saved and what you add each month, and this calculator works out how long until you get there, the date that lands on, and your coast FIRE number — the amount that could grow the rest of the way on its own. Everything runs in your browser; the defaults are the worked example.
The model: FIRE number = annual expenses (after the lifestyle multiplier) ÷ safe withdrawal rate. Years to FIRE comes from a monthly simulation: each month your balance grows at (1 + return)1/12 − 1 and your contribution is added at month end, until the balance reaches the FIRE number (searched up to 100 years). Coast FIRE = FIRE number ÷ (1 + return)retirement age − current age.
The projected date counts forward from today using the months the simulation needs. Returns are modelled as a smooth average — real markets arrive in lumps, so treat the date as a planning estimate, not a promise. Taxes, fees and inflation are not modelled; many planners use a return figure net of inflation so the target stays in today's money.
The same monthly simulation, stopped at each milestone. Half FIRE and coast FIRE are the two points where your options change: at coast, contributions become optional if you are willing to wait until your retirement age.
| Milestone | Amount | Reached in | Projected date |
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Your FIRE number from expenses and safe withdrawal rate — plus years to FIRE, projected FIRE date, coast FIRE number and milestone dates.
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Work out your FIRE number — the portfolio that can fund your retirement — from your annual expenses and a safe withdrawal rate, then see how many years of saving and growth it takes to get there, the date that lands on, and your coast FIRE number: what you would need today for growth alone to finish the job by your retirement age.
Your retirement spending is $48,000 a year and you use a 4% safe withdrawal rate, so your FIRE number is $48,000 ÷ 0.04 = $1,200,000 exactly. With $150,000 already invested, $1,500 a month of contributions and 7% annual returns, the monthly simulation reaches $1,200,000 in 224 months — about 18.7 years. Your coast FIRE number at age 30 retiring at 65 is $1,200,000 ÷ 1.07^35 ≈ $112,396, so with $150,000 invested you are already past coast FIRE: even if contributions stopped, growth alone would be projected to reach the target by 65.
FIRE number = annual expenses (after the lifestyle multiplier) ÷ safe withdrawal rate as a decimal. Years to FIRE is found by a monthly simulation, not a formula: each month the balance grows at (1 + annual return)^(1/12) − 1 and the monthly contribution is added at month end, until the balance first reaches the FIRE number (searched up to 100 years; the projected date counts those months forward from today). Coast FIRE = FIRE number ÷ (1 + annual return)^(retirement age − current age) — the amount that needs no further contributions to grow into the full FIRE number by the retirement age. Progress = current savings ÷ FIRE number.
The size of portfolio that can pay your annual expenses indefinitely at your chosen safe withdrawal rate: expenses ÷ withdrawal rate. At $48,000 of spending and 4%, that is $1,200,000 — the point where investment income, not a salary, covers your life, and work becomes optional.
It is the divisor, so small changes move the target a lot: at 4% you need 25× annual expenses, at 3.5% about 28.6×, at 3% about 33.3×. A lower rate means a bigger target but a portfolio that historically survives more bad sequences of returns.
The amount you need invested today so that compound growth alone — with no further contributions — reaches your full FIRE number by your chosen retirement age. Crossing it means your savings habit could stop and the plan would still land on time; everything you add after only pulls the date earlier.
Lifestyle variants of the same target. Lean FIRE scales expenses down (here ×0.75) for a stripped-back retirement and a much smaller, earlier number; Fat FIRE scales them up (×1.25) for a generous one. They are the same formula with different spending assumptions.
The calculator simulates month by month: the balance grows at the monthly equivalent of 7% a year (about 0.5654% a month) and $1,500 is added at each month end. Starting from $150,000, the balance first passes $1,200,000 at month 224 (about 18.7 years), ending that month at roughly $1,203,130; at month 223 it is still about $1,194,831 — short of the target.
That is a common and comfortable position: your existing investments are projected to finish the job by your retirement age even if you never add another dollar. Continuing to contribute does not change the destination — it changes the date, pulling full FIRE earlier than the retirement age.
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