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?
The point where your portfolio can grow to fund retirement with no further contributions. You still work to cover current expenses, but compounding handles the retirement target by itself.
How do you calculate your Coast FIRE number?
FI number = spending divided by safe withdrawal rate ($40,000 / 4% = $1,000,000). Coast number = FI number / (1 + real return)^years to retirement. At 7% over 30 years: about $131,367.
What real return should I use?
7% is the long-run inflation-adjusted stock market average and the default here. Use 5% or 6% for a more conservative or bond-heavy plan; the coast number rises as the return falls.
Is the 4% safe withdrawal rate reliable?
It is a historical rule of thumb for 30-year retirements, not a guarantee. Longer horizons often call for 3.25% to 3.5%, which raises both the FI number and the coast number. Set any rate you like above.
Is this Coast FIRE calculator free?
Yes. Free, no sign-up, and every calculation runs locally in your browser. Nothing you type is uploaded.