Coast FIRE Calculator
Find the portfolio size at which compounding alone can fund your retirement, and see whether you are already there.
All figures are in today's dollars because the return input is real (after inflation). Contributions are assumed to be invested at year-end.
Coast FI age assumes contributions continue as entered. With contribution set to 0, it is the age where growth alone closes the gap.
What is Coast FIRE?
Coast FIRE is the milestone where your invested portfolio is big enough to fund your retirement without another dollar of contributions, as long as you leave it invested until your target retirement age. You are not financially independent yet, because you still need income for today's bills. But the retirement problem is solved by compounding, so you can coast: take a lower-stress job, work part time, or simply stop saving without endangering your future. It is a psychologically powerful waypoint because it arrives far earlier than full FI, often a decade or more sooner.
The math behind your coast number
Start with your FI number, the portfolio that funds retirement: annual spending divided by your safe withdrawal rate. Spending $40,000 a year at a 4% rate means a $1,000,000 target. Then ask: how much would I need invested today for growth alone to reach that target? Discount the FI number back by your expected real return over the years until retirement: coast number = FI number / (1 + r)^years. At a 7% real return with 30 years to go, that is about $131,367. A 30-year-old with more than that invested is already at Coast FI; anyone below it sees the exact gap and, if contributions continue, the age at which the growing portfolio crosses the shrinking coast line.
Small input changes move the answer a lot. Dropping the return assumption from 7% to 5% roughly doubles the coast number over 30 years, and cutting the withdrawal rate from 4% to 3.5% raises the FI number by 14%. Treat the output as a planning estimate: real markets do not deliver smooth 7% years, so many people add a margin of safety before declaring themselves done saving.
Frequently asked questions
What is Coast FIRE?
Coast FIRE is the point where your invested portfolio is already large enough that, with no further contributions, it can grow to fund your retirement by your target retirement age. Once you reach it, you only need to earn enough to cover current living expenses, and every retirement dollar is already handled by compounding. It sits between a traditional savings path and full financial independence.
How do you calculate your Coast FIRE number?
First get your FI number: target annual retirement spending divided by your safe withdrawal rate. At $40,000 of spending and a 4% rate, that is $1,000,000. Then discount it back to today: coast number = FI number / (1 + real return)^(years to retirement). At a 7% real return with 30 years to go, the coast number is about $131,367. If your portfolio already exceeds it, you are at Coast FI.
What real return should I use?
The default 7% is the long-run inflation-adjusted return of a diversified stock portfolio, and using real (after-inflation) returns keeps everything in today's dollars. If you hold more bonds or want a conservative margin, try 5% or 6%. The coast number rises quickly as the assumed return falls, because your portfolio has to do more of the work itself.
Is the 4% safe withdrawal rate reliable?
The 4% rule comes from historical studies showing a portfolio survived 30-year retirements when withdrawals started at 4% and rose with inflation. It is a planning rule of thumb, not a guarantee: early retirees with 40 or 50 year horizons often use 3.25% to 3.5%, which raises the FI number and therefore the coast number. This calculator lets you set any rate you like.
Is this Coast FIRE calculator free?
Yes. It is completely free, requires no sign-up, and all calculations run locally in your browser. Nothing you type is uploaded anywhere.