How the Coast FIRE number is calculated
First the calculator finds your full FIRE number: the portfolio that supports your retirement spending at your chosen withdrawal rate. Then it works backwards, discounting that number by the growth you’d expect between now and your retirement age.
All figures are in today’s dollars, which is why the return should be after inflation. A 5% real return is a moderate assumption for a stock-heavy portfolio; using a nominal 10% would badly overstate your progress.
What this simple version leaves out
It ignores taxes on withdrawals, health insurance before Medicare and Social Security. For a fuller picture that includes all three, use the Coast FIRE tab in the full calculator. To understand the concept and its risks, read What is Coast FIRE?
Common questions
What return should I use?
A return after inflation, since everything is in today’s dollars. 4–6% is a common range for a mostly-stock portfolio; 5% is a reasonable middle.
Should I really stop saving once I hit Coast FIRE?
You can, but many people keep saving a little as a buffer against weak markets, or use Coast FIRE as permission to take a lower-paying job they enjoy more.
Estimates for education only, not financial or tax advice. 2026 tax-year rules and limits; check the details with your plan provider or a tax professional.