FIRE Number Calculator
Calculate how much you need to retire using the 4% (25x) rule for financial independence.
How to use this tool
- Enter annual expenses in retirement, safe withdrawal rate, current savings / investments, annual contribution and expected annual return in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your fire number needed and the full breakdown beneath it.
The 4% rule (25x rule) states you can safely withdraw 4% of your portfolio per year in retirement. Your FIRE number is 25× your annual expenses.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
FIRE Number = Annual Expenses ÷ (Safe Withdrawal Rate ÷ 100)
Savings Gap = max(0, FIRE Number − Current Savings)
Years to FIRE (with contributions & growth): iteratively compound balance = balance × (1 + r) + Annual Contribution until balance ≥ FIRE Number, where r = Expected Annual Return ÷ 100.
How it works
The FIRE number is derived from the safe withdrawal rate (SWR) concept: the annual portfolio withdrawal divided by the total portfolio value. At a 4% SWR the FIRE number equals 25× annual expenses — the classic guideline from the Trinity Study. Years to FIRE is estimated by iterating year-by-year portfolio growth at the expected return, adding annual contributions each period until the balance reaches the FIRE number. This approach assumes a constant real return and fixed contribution rate; actual results will vary with market performance, inflation, and lifestyle changes.
Worked example
- Annual retirement expenses: $40,000. Safe withdrawal rate: 4%. Current savings: $100,000. Annual contribution: $0. Expected return: 0%.
- FIRE number = $40,000 ÷ 0.04 = $1,000,000.
- Savings gap = max(0, $1,000,000 − $100,000) = $900,000.
FIRE number: $1,000,000 | Savings gap: $900,000
Common mistakes to avoid
- Using current spending rather than projected retirement spending as the annual expenses input, ignoring that costs like commuting or work lunches may fall after retiring.
- Applying the 4% rule to a 40-year retirement when research suggests a lower withdrawal rate (3-3.5%) is safer for retirements lasting 40+ years.
- Forgetting to include expected Social Security or pension income, which reduces the savings gap and can dramatically lower the FIRE number.
Key terms
- FIRE number
- The total investment portfolio value required to retire, calculated so that annual withdrawals at the safe withdrawal rate cover all living expenses indefinitely.
- Safe withdrawal rate (SWR)
- The percentage of a portfolio withdrawn annually that historical data suggests a portfolio can sustain for 30+ years; commonly set at 4% based on the Trinity Study.
- Trinity Study
- A 1998 academic paper by three Trinity University professors analyzing historical U.S. stock and bond returns to determine sustainable retirement withdrawal rates.
- Coast FIRE
- A FIRE variant where you have saved enough that investment growth alone — without further contributions — will reach your FIRE number by traditional retirement age.
- Sequence of returns risk
- The danger that poor investment returns early in retirement permanently deplete a portfolio, even if long-run average returns are adequate.
Frequently asked questions
- What is the 4% rule?
- The 4% rule, derived from the Trinity Study, suggests you can withdraw 4% of your initial retirement portfolio per year (adjusted for inflation) with a high probability that your money lasts 30+ years.
- Can I use a different withdrawal rate?
- Yes. More conservative retirees use 3% or 3.5% (higher FIRE number). Those with other income sources or flexible spending may use 5%. Adjust the safe withdrawal rate field accordingly.