Where does the '4% rule' come from?

William Bengen's 1994 study and the 1998 Trinity Study, both testing historical U.S. market returns over rolling 30-year periods, found withdrawing about 4% rarely depleted a portfolio within 30 years.

Is the 4% rule guaranteed to work?

No — it's based on historical U.S. market backtests, not a guarantee about future markets, and doesn't account for taxes, fees, or poor early-retirement returns.

Why does a lower withdrawal rate require more savings?

The FIRE number is expenses divided by the withdrawal rate — a smaller rate produces a bigger required number.

Does this account for inflation?

No — it assumes today's annual expenses stay constant in nominal terms.

What return should I assume?

There's no single right answer — a diversified stock/bond portfolio has historically returned roughly 6-8% nominally over long periods, but outcomes vary.

Does 'years to FIRE' include Social Security or a pension?

No — this calculator only projects your own savings and contributions.

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Finance

FIRE Calculator

Your FIRE number and years to financial independence at a chosen withdrawal rate.

🔒 Runs entirely in your browser — nothing here is ever uploaded

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Last reviewed 2026-08-30

About the FIRE Calculator

Estimates your 'FIRE number' (the invested savings needed to support your annual expenses at a chosen safe withdrawal rate) and projects how many years of current savings and contributions, compounding at an assumed return, it would take to reach it.

100% Free Runs in Your Browser No Sign-Up Required

How to use it

Enter your Current savings and Annual expenses.
Enter your Annual savings (new contributions) and Expected annual return.
Choose a Withdrawal rate — 4% is the classic 'rule.'
Read your FIRE number, years to FIRE, and today's progress percentage.

Formula

FIRE number = Annual expenses ÷ Withdrawal rate (e.g. at 4%, FIRE number = 25 × annual expenses). Projected savings after n years = current savings × (1+r)^n + annual contributions × (((1+r)^n − 1) ÷ r), solved iteratively year-by-year (capped at 60 years) to find the first year the projection meets or exceeds the FIRE number.

Worked example

$150,000 in current savings, $48,000/yr expenses, $30,000/yr new savings, 7% expected return, and the classic 4% withdrawal rate: FIRE number = $1,200,000, reached in about 16 years.

Common withdrawal rate assumptions

Common withdrawal rate assumptions
Rate	FIRE number = expenses ×	Basis
3.0%	33.3	Conservative, common for very long (40+ year) retirement horizons
3.5%	28.6	William Bengen's own 1994 estimate for a 40-year horizon
4.0%	25	The classic 'safe withdrawal rate,' from the 1994 Bengen study and 1998 Trinity Study
4.5%	22.2	Bengen's later, more optimistic revision assuming a more diversified portfolio

Interpreting your result

Assumes a constant annual return every year, which real investment returns never actually deliver. Ignores taxes, inflation eroding future expenses, and other income sources like Social Security. The withdrawal rate is a widely used planning heuristic from historical U.S. market backtests, not a mathematical guarantee.

Recommendations

• A lower withdrawal rate means a bigger required FIRE number but more cushion against poor market sequences early in retirement (sequence-of-returns risk).
• Small increases in annual savings rate typically shorten years-to-FIRE more than chasing a higher expected return.
• This tool ignores inflation — your annual expenses (and FIRE number) will likely rise over the years you're saving.

Frequently asked questions

Financial Independence, Retire Early — saving and investing aggressively enough to cover living expenses from investment income well before traditional retirement age.