Financial Independence, Retire Early

FIRE calculator

Find your FIRE number, projected years to financial independence, and which FIRE flavor — Lean, Fat, or Coast — fits your numbers. Free, no sign-up.

Or run it as a growth projection

Same inputs in a generic compound-growth view if you want to model alternate scenarios.

The FIRE formula

FIRE number = 25 × annual expenses
Years to FIRE ≈ ln(1 + (FIRE × r) / (12 × PMT)) / ln(1 + r)

Where:
  r   = annual real return (e.g., 0.07 for 7%)
  PMT = monthly savings

Types of FIRE

Flavor	Annual spending	FIRE number	Notes
Lean FIRE	<$40k	<$1.0M	Frugal living, geo-arbitrage
Regular FIRE	$40k–$100k	$1.0M–$2.5M	Standard middle-class FIRE
Fat FIRE	>$100k	>$2.5M	Comfortable / luxury retirement
Coast FIRE	Cover today only	Less, but invested early	No more retirement contributions needed
Barista FIRE	Part-time job covers gap	~50% of FIRE	Health insurance via part-time work

Savings rate vs years to FIRE

From Mr. Money Mustache's classic table — assuming 5% real returns and a 4% SWR, starting from zero:

15% savings rate: 43 years
25% savings rate: 32 years
40% savings rate: 22 years
50% savings rate: 17 years
65% savings rate: 10.5 years
75% savings rate: 7 years
85% savings rate: 4 years

Coast FIRE explained

Coast FIRE = invest enough early that compound growth alone hits your FIRE number by age 65. After Coast FIRE you only need to cover current expenses; you never need to save for retirement again. Coast FIRE number = FIRE number ÷ (1 + r)^(65 − current_age).

Example: 30-year-old wanting $1.5M at 65 with 7% real return needs $1.5M / 1.07^35 ≈ $140,500 invested today to coast.

FIRE calculator FAQ

What is FIRE?

FIRE stands for Financial Independence, Retire Early. The movement promotes high savings rates (40–70% of income) invested in low-cost index funds, with the goal of accumulating 25× annual expenses so you can live off a 4% withdrawal rate indefinitely.

What's my FIRE number?

Your FIRE number is 25× your annual expenses. If you spend $40,000/year, your FIRE number is $1,000,000. If you spend $80,000/year, it's $2,000,000. This is based on the 4% safe withdrawal rate from the Trinity Study.

What's the difference between Lean FIRE, Fat FIRE, and Coast FIRE?

Lean FIRE is retiring on under $40,000/year of spending. Fat FIRE is retiring on over $100,000/year. Coast FIRE is having enough invested so that, without adding another dollar, compounding alone reaches your full FIRE number by traditional retirement age — you can 'coast' by covering current expenses only.

How fast can I reach FIRE?

At a 50% savings rate with 7% real returns, you reach FIRE in about 17 years from a $0 start — regardless of income level. At 65%, ~11 years. At 75%, ~7 years. Savings rate is the single biggest lever; income matters less than people think.

Is the 4% rule still safe?

Bengen's original 4% safe withdrawal rate had ~95% success over 30 years. For 40–50 year retirements (typical for FIRE), most planners suggest 3.25–3.5% to add a safety margin, plus flexibility to reduce spending in bad years.

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Project any rate, any horizon.

Sources & methodology

FIRE math, the 4% rule, and long-run return assumptions are grounded in these authoritative sources. Last verified 2026-06-15.

Trinity Study (Cooley, Hubbard, Walz — 1998) — original research establishing the 4% safe withdrawal rate.
Robert Shiller (Yale) — S&P 500 historical returns dataset (1871–present) — primary academic source for 10% nominal / 7% real long-run averages.
Early Retirement Now — Safe Withdrawal Rate Series (Karsten Jeske) — most rigorous academic-style analysis of SWR with sequence-of-returns risk.
U.S. Bureau of Labor Statistics — CPI — inflation series used to convert nominal returns to real returns.
SPIVA Scorecard (S&P Dow Jones Indices) — research showing why long-run index returns are the right input for FIRE planning.
Mr. Money Mustache — The Shockingly Simple Math Behind Early Retirement (2012) — popularized the savings-rate-to-retirement-years mapping that drives FIRE planning.

Methodology: FIRE number = annual expenses × (100 / SWR). At 4% SWR that's 25×. Years-to-FIRE solved via future-value-of-annuity formula with monthly compounding. Coast FIRE = FIRE number ÷ (1 + r)^(years to 65). No fees deducted — enter your real return net of expense ratios. Cross-validated against the Engaging Data FIRE calculator and WalletBurst FIRE calculator.