FIRE calculator

How it works

Your FIRE number is the amount you need invested for its returns to pay your spending:

FIRE number = monthly spending × 12 / withdrawal rate

At a 4% withdrawal rate that is 25 times your yearly spending. The calculator then grows your investments month by month at the real return you enter, adds your monthly contribution, and counts the months until the balance reaches the FIRE number:

balance next month = balance × (1 + r / 12) + contribution

A worked example

You expect to spend 3,000 a month, or 36,000 a year. At 4%, your FIRE number is 36,000 / 0.04 = 900,000. With 50,000 invested, 1,500 added each month and a 5% real return, the balance passes 900,000 after about 22.6 years (271 months).

Assumptions to check

• Use a real return, after inflation, because your spending is in today's money. A 7% market return with 2% inflation is about 5% real. The inflation calculator shows why it matters.
• The 4% withdrawal rate comes from US research on 30-year retirements. If you plan to stop much earlier, a lower rate such as 3.5% gives you more margin.
• Returns are steady here; real ones are not. Taxes and pension rules are not modelled.

New to FIRE? Read the practical guide to the FIRE movement. To see when you could stop saving and let growth do the rest, try the Coast FIRE calculator.