Coast FIRE Calculator
See whether the money you have already invested can coast — growing on its own into a full retirement without another dollar of saving.
How to use this calculator
Enter your current age and the age you plan to retire — the gap between them is how long your money has to grow. Add the amount you have invested today, the real return you expect (returns after inflation), your annual spending in retirement, and the withdrawal rate you plan to live on. The result shows your Coast FIRE number: the balance you would need invested right now so that, with zero further contributions, it grows into your full retirement nest egg by your target age.
How this is calculated
First we find your full FIRE number — annual expenses divided by your withdrawal rate (a 4% rate means you need 25× your spending). Then we discount that target back to today using your expected real return over the years until retirement. That discounted figure is your Coast FIRE number. We also project what your current balance will become by retirement: if that projection already meets or beats the FIRE number, you have reached Coast FIRE and could stop saving for retirement entirely.
Educational estimate, not investment advice — see our disclaimer.
A worked example
Suppose you are 30, want to retire at 65, and expect a 5% real return. You spend $40,000 a year and plan on a 4% withdrawal rate, so your full FIRE number is $40,000 ÷ 0.04 = $1,000,000. With 35 years to grow, money roughly multiplies 5.5× at 5% real, so you only need about $185,000 invested today for it to coast to a million. If you already have $185,000 or more, you have hit Coast FIRE — your retirement is funded and every future dollar you save is gravy. If you have less, the calculator shows exactly how much more you would need invested today to close the gap.
Why Coast FIRE is liberating
Coast FIRE is the moment your retirement stops depending on future saving. You still need income to cover today's bills, but you no longer have to set aside a cent for the far-off future — compounding does the rest. That can mean switching to a lower-stress job, going part-time, taking a sabbatical, or pouring savings into nearer-term goals like a home or travel instead. Hitting Coast FIRE early, in your late twenties or thirties, buys decades of flexibility. Our FIRE calculator shows the full picture if you would rather retire outright rather than coast.
Common mistakes to avoid
- Using nominal returns — always enter a real (after-inflation) return so your future number is in today's dollars.
- Forgetting current expenses — Coast FIRE only frees up retirement saving; you still need to earn enough to live on now.
- Assuming a smooth ride — markets fall as well as rise, so revisit the numbers if a downturn dents your balance.
- Setting an aggressive withdrawal rate — a higher rate lowers your target but raises the risk of running out later.
Once you know your target, a compound interest calculator can show year-by-year how today's balance grows on its own.