Calculate your FIRE number, years to financial independence, and safe withdrawal rate. Supports Lean FIRE, regular FIRE, and Fat FIRE. 2026 US data included. Free.
The Math Behind FIRE
FIRE stands for Financial Independence, Retire Early. The movement is built on one equation: invest until your portfolio is 25× your annual spending, then withdraw 4% per year indefinitely. The 4% rule was established by the Trinity Study (1998) showing a 95%+ survival rate for 30-year retirements with a balanced portfolio.
Savings Rate Is Everything
Your savings rate determines your FIRE timeline more than any other variable. A 50% savings rate means you can retire in roughly 17 years from zero. Why? Because every dollar saved does double duty: it adds to your portfolio AND reduces future spending (lower expenses = smaller FIRE number). The corollary: lifestyle creep is the biggest enemy of early retirement.
Savings Rate
Years to FIRE (from zero)
10%
~43 years
25%
~32 years
50%
~17 years
65%
~11 years
75%
~7 years
Tax-Advantaged Accounts and FIRE
Max your 401(k) ($24,500 in 2026) and Roth IRA ($7,500) before taxable investing. At early retirement ages (40s or 50s), you can’t access 401(k) funds penalty-free until 59½ — use a Roth conversion ladder to bridge the gap. Build enough in taxable brokerage accounts to cover 5 years of expenses while your Roth conversions season.
Your FIRE number is the amount you need invested to retire — defined as 25× your annual expenses (based on the 4% safe withdrawal rate). If you spend $60,000/year: $60,000 × 25 = $1,500,000 FIRE number. At 4% withdrawal, $1,500,000 generates $60,000/year in income, and historical data suggests this portfolio has roughly 95% probability of lasting 30 years. The 4% rule comes from the Trinity Study using 1926–1995 US stock and bond data.
The 4% rule has held up historically but faces scrutiny at current valuations. Some planners advocate 3%–3.5% for longer retirements (40+ years) or those retiring in their 30s–40s. At 3.5%, your FIRE number on $60,000/year becomes $1,714,000 vs $1,500,000. The key variables: sequence of returns risk (bad markets in years 1–5 are most damaging), inflation rate, and actual portfolio allocation. A 60/40 stock-bond split with annual rebalancing is the standard assumption.
Lean FIRE: retiring on $40,000/year or less, requiring a frugal lifestyle. FIRE number: roughly $1,000,000. Regular FIRE: $50,000–$100,000/year in spending. FIRE number: $1,250,000–$2,500,000. Fat FIRE: $100,000+/year spending without financial stress. FIRE number: $2,500,000+. Chubby FIRE ($80,000–$120,000/year) sits between regular and fat. Which level you target depends entirely on your actual spending — build the budget first, then calculate the number.
It depends almost entirely on your savings rate — not your income. On a $80,000 salary, saving 10% ($8,000/year) takes about 43 years to hit 25× $64,000 expenses. Saving 30% ($24,000/year) reduces expenses to $56,000 and takes about 28 years. Saving 50% ($40,000/year) reduces expenses to $40,000 and takes about 17 years. The math: higher savings rate simultaneously grows your portfolio faster and reduces the FIRE number (because lower expenses = lower FIRE number). Every 1% savings rate increase accelerates FIRE noticeably.
Most FIRE community planners use 7% nominal (roughly 4% real after inflation) for a broadly diversified stock portfolio. Conservative projections use 5%–6%. The actual S&P 500 historical average is about 10% nominal / 7% real. Using 7% nominal is reasonable for a 70%–80% equity allocation. For FIRE projections with a 30–40 year horizon, the real return (after inflation) matters most — use 4%–5% real return to be conservative.
