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Retirement and FIRE calculator

FIRE means financial independence, retire early. Enter what you spend, what you have invested and what you save each month to see the amount that could pay for your life — your FIRE number — and how long it takes to get there, with a chart and every step explained.

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  • Private — runs in your browser

How do I calculate my FIRE number?

  1. 1Enter the spending you want to cover, per month or per year, in today's money.
  2. 2Pick a safe withdrawal rate — 4% is the classic rule, 3–3.5% is more careful.
  3. 3Enter what you have invested today, what you add each month and the growth you expect after inflation.
  4. 4Read your FIRE number, the time and age you reach it, the chart and the year-by-year table.

How is the time to financial independence worked out?

  1. 01FIRE number = yearly spending ÷ withdrawal rate (4% → spending × 25)
  2. 02Monthly growth i = (1 + yearly growth after inflation)^(1/12) − 1
  3. 03Investments after n months = P × (1 + i)ⁿ + C × ((1 + i)ⁿ − 1) ÷ i
  4. 04Months to FIRE n = ln((T × i + C) ÷ (P × i + C)) ÷ ln(1 + i)
  5. 05P = invested today · C = saved each month · T = FIRE number

Your FIRE number is the pot of investments that could pay your yearly spending for the rest of your life. With the 4% rule you divide your spending by 0.04 — the same as multiplying by 25. Spending 36,000 a year needs about 900,000; spending 12,00,000 a year needs 3,00,00,000.

The growth you enter is the average yearly profit from investments such as shares, funds or property, after taking off inflation. Because inflation is already removed, every amount on this page is in today's money, and your spending doesn't need to be raised for future prices.

Each month your investments grow a little and you add your saving. The calculator works out exactly when the total first reaches your FIRE number, using the formula for regular savings growing at a steady rate.

Real markets don't grow steadily: some years fall sharply. The 4% rule was tested on that bumpy US history, which is why it is a little careful — but not a guarantee, especially for retirements longer than 30 years.

Good to know

  • Your savings rate matters most: spending less both lowers your FIRE number and raises what you save.
  • Use a careful growth figure (3–5% after inflation) — a plan that only works at 8% is fragile.
  • Count every yearly cost in your spending: insurance, health care, repairs, gifts, travel and charity.
  • Re-run the plan once a year with your real numbers.

FIRE and early retirement questions

What is a FIRE number?

The amount of invested money that could pay your yearly spending for good. Using the 4% rule it is your yearly spending × 25 — for example 40,000 a year needs 1,000,000.

What is the 4% rule?

A rule of thumb from studies of US markets since 1926 (Bengen 1994, the Trinity study 1998): take 4% of your savings in the first year of retirement, then raise that amount with inflation each year. In the past this lasted at least 30 years in about 95% or more of cases for portfolios at least half in shares.

Is 4% safe for early retirement?

It was tested for 30 years. If you retire at 40 your money may need to last 50 years or more, so many people use 3–3.5% (spending × 29 to × 33) and stay ready to spend a little less after bad market years.

How much do I need to retire early?

About 25 to 33 times the yearly spending you want to cover, depending on the withdrawal rate. Spending 3,000 a month (36,000 a year) needs about 900,000 at 4% or 1,028,571 at 3.5%.

Why does the calculator use growth after inflation?

So that every amount stays in today's money. If investments make 8% a year and prices rise 3%, the real growth is about 5%. Your FIRE number then stays the same in today's prices, and you don't have to guess future prices.

What are Lean FIRE and Fat FIRE?

Lean FIRE plans for a simple, low-cost life, so the FIRE number is smaller and reached sooner. Fat FIRE plans for a comfortable or generous lifestyle, which needs a much larger pot. The maths is the same — only the spending changes.

Sources

Formulas last reviewed: September 30, 2026 ·How we check our formulas

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