How Coast FIRE works
Enter the age when you want to start retirement withdrawals. The calculator finds how much you need invested today to reach that target without further contributions. It also estimates when contributions could stop if you keep saving until then.
You still need income to cover living expenses while coasting. The portfolio-at-retirement figure separately shows the result if you keep contributing until retirement.
Reproduce a Coast FIRE example
At age 35, choose retirement at 65, annual spending of 40,000 and a 4% withdrawal rate. The retirement target is 1,000,000. At a 4% real return for 30 years, the coast threshold today is 1,000,000 ÷ 1.0430 = 308,319.
To reproduce this real-return example, use 4% return, 0% inflation and monthly spending of 3,333.333333. A portfolio of 320,000 exceeds the threshold with no more contributions. A portfolio of 200,000 does not; planned future contributions do not mean you have reached Coast FIRE today.
How the saving-stop age is calculated
Each month, the portfolio earns the real monthly return and receives the contribution. We compare it with the target discounted over the remaining months until the retirement age you entered. Contributions can stop at the first month that reaches that moving threshold. If no month qualifies, the result is “Not reached”.
Return is entered before inflation. Contributions and spending are in today’s money. A zero return or zero inflation is a valid input. Full calculation conventions.
Test the risk in the assumption
The example threshold rises from 308,319 to about 552,071 if the real return falls from 4% to 2%. That is why a long coast period is sensitive to assumptions. Tax, fees, interrupted income and changing spending can also change the result.
Coast FIRE is about retirement contributions, not the ability to pay current bills from the portfolio. If withdrawals start now, use the retirement backtest instead.