How we calculate

Every calculator on this site runs in your browser. Here is exactly what it does.

Today's dollars

All amounts are in today's dollars, and growth uses a real return, meaning after inflation. That's why the default is 5% and not the 7–10% you often see for stocks.

FIRE number

FIRE number = yearly spending ÷ withdrawal rate. At 4%, that's 25 × spending. The 4% rate comes from studies of 30-year retirements using US market history; longer retirements usually call for 3.25–3.5%.

Coast FIRE

The Coast FIRE line at age a is the FIRE number discounted back from your retirement age: FIRE number ÷ (1 + r)^{retirement age − a}. We simulate your portfolio month by month with your yearly savings spread evenly, and the Coast FIRE age is the first month your balance reaches that line.

FIRE date

Savings = take-home income − spending. The portfolio grows monthly at the real return plus one twelfth of yearly savings until it reaches the FIRE number. We stop at 60 years.

Barista FIRE

"Needed today" is the present value of two things: each year's gap (spending + health insurance before 65 − part-time income) until part-time work stops, and the full FIRE number at that age. The rule-of-thumb figure is simply the first year's gap ÷ withdrawal rate.

72(t)

Life expectancy comes from the IRS Single Life Expectancy table in effect since 2022 (Publication 590-B, Appendix B, Table I). The RMD method is balance ÷ life expectancy. The amortization method is balance × i ÷ (1 − (1 + i)⁻ⁿ), with n the life expectancy and i your interest rate, capped by the IRS at the greater of 5% or 120% of the federal mid-term rate (Notice 2022-6).

What we leave out

Taxes, fees, Social Security, pensions and market swings. These calculators are for planning ranges, not exact forecasts. Questions about a formula: hello@coastfire.pro.