Coast FIRE calculator

What Coast FIRE means

Coast FIRE is the point where you have invested enough today that, even if you never contribute another dollar, compound growth alone will carry your portfolio to your full FIRE number by the time you retire. It is one of the most liberating milestones on the path to financial independence, because it arrives years before you actually have enough to retire.

The math

This calculator works backward from your destination:

1. Full FIRE number = annual spending ÷ safe withdrawal rate.
2. Coast number = that FIRE number discounted back to today at your expected real return, over the years until retirement.

The longer you have until retirement, the smaller your Coast number - because compounding has more time to do the work.

Worked example

A 30-year-old planning to retire at 60, spending $80,000 a year, at a 4% withdrawal rate and a 5% real return:

• Full FIRE number: $80,000 ÷ 4% = $2,000,000
• Coast number today: $2,000,000 discounted 30 years at 5% = about $462,755
• With $200,000 invested, you are not yet coasting - you need roughly $262,755 more before you could stop contributing.

If that same person already had $462,755 invested, they could stop saving for retirement entirely and still reach $2M by 60, just by covering their current bills.

Why it is powerful

Coast FIRE separates “saving for retirement” from “paying for today.” Once you hit your Coast number you can:

• Downshift to a lower-stress or part-time job that only covers current expenses.
• Take more career risk - a startup, a sabbatical, a career change.
• Redirect future savings toward nearer-term goals instead of retirement.

How to use the result

Move your retirement age and return assumptions to see how the Coast number shifts. A more conservative return (say 4%) raises the number; a longer runway lowers it. Treat the figure as a planning estimate - markets are volatile, so many people keep contributing a while past their Coast number as a buffer.

Common mistakes

• Using an optimistic return that makes the Coast number look closer than it is.
• Forgetting that the number is in today’s dollars - use a real return, not a nominal one.
• Stopping all saving the moment you hit it, with no margin for a bad market.

To model the full picture, see the FIRE calculator; for a semi-retirement variant where part-time income covers part of your spending, see the Barista FIRE calculator.