FIRE & Retirement Calculators

A FIRE number is the portfolio size at which investment withdrawals can cover annual spending, and it comes from one division: annual spending ÷ withdrawal rate. At a 4% withdrawal rate that works out to 25× annual spending (1 ÷ 0.04 = 25); at 3.5% it is roughly 28.6×. The FIRE Number calculator computes that target from your own spending and withdrawal-rate inputs, then projects how many years your current savings plus ongoing contributions take to reach it at a growth rate you set.

Coast FIRE is the present value of that same target: the amount which, invested today and left untouched, would grow into your full FIRE number by a traditional retirement age with no further contributions. The Coast FIRE calculator computes that threshold for your age and target, then checks your current savings against it. Crossing it does not mean work is optional now — it means the retirement-savings part of the problem is mathematically on autopilot, and future income only has to cover current spending.

Both tools deliberately leave the contested assumptions to you. The withdrawal rate is an editable input because the common 4% figure comes from historical U.S. market studies and is debated, particularly for retirements longer than the 30 years those studies assumed. The growth-rate input is best treated as a real, after-inflation return, since spending is entered in today’s dollars — mixing a nominal return with today’s spending overstates the result. Small input changes move the answers a lot, which is the point: these calculators are built for re-running scenarios, not for producing one fixed number. Start with the FIRE Number tool to establish the target, then use Coast FIRE to see how much of it today’s savings already cover; the table below summarizes both.