What is a FIRE number?
In the FIRE movement (Financial Independence, Retire Early), your FIRE number is the amount you need invested so that withdrawals can pay for your life indefinitely. Once you reach it, a paycheck becomes optional.
The idea rests on the safe withdrawal rate: the share of your portfolio you can withdraw in the first year (then adjust for inflation) with a high probability of not running out. The best-known figure is 4%, which comes from research on historical US stock and bond returns over 30-year retirements.
How this calculator works
Real return = (1 + nominal return) ÷ (1 + inflation) − 1
Each month: portfolio = portfolio × (1 + monthly real return) + monthly investing
It finds the first month where your projected portfolio reaches the FIRE number. Because it uses a real return, every figure is in today's dollars, so your target stays the same as you age instead of drifting with inflation. That's why the FIRE number line on the chart is flat.
The table under the chart shows how much your target and timeline change at different withdrawal rates, so you can see the cost of extra safety.
Worked example
You're 30, expect to spend $45,000 a year, have $80,000 invested and invest $2,000 a month. At a 4% withdrawal rate your FIRE number is $45,000 ÷ 0.04 = $1,125,000. With a 7% return and 3% inflation, you'd reach it in about 23 years and 10 months, around age 54.
A more cautious 3.5% withdrawal rate raises the target to about $1.29 million and adds a little over two years. At 3%, the target is $1.5 million and you'd need about 29 years.
Ways to reach FIRE sooner
- Lower your expenses. This works twice: it shrinks your target (every $1,000 a year less cuts $25,000 at 4%) and frees up more to invest.
- Raise your savings rate. Try increasing the monthly investing amount to see how many years each extra $500 is worth.
- Plan for other income. A pension, rental income, part-time work or future Social Security reduces what your portfolio must cover. Subtract it from your expenses.
- Consider Coast FIRE. You may not need to save until your full number. Our Coast FIRE calculator shows when you could stop saving and let growth do the rest.
Limitations
Real markets don't deliver steady average returns, and early retirees face long horizons and sequence-of-returns risk. The calculator also doesn't model taxes, account access rules or changing spending in retirement. Use it to set a target and track progress, and revisit it yearly.
Frequently asked questions
What is a FIRE number?
Your FIRE number is the portfolio size that lets you cover your yearly living expenses from investment withdrawals indefinitely, so work becomes optional. The common shortcut is 25 times your annual expenses, which corresponds to a 4% withdrawal rate.
Why 25 times expenses?
Dividing your expenses by a 4% withdrawal rate is the same as multiplying them by 25. A 3.5% rate means about 28.6 times expenses and a 3% rate means about 33.3 times. Lower rates build in more safety, especially for retirements longer than 30 years.
Should I use today's expenses or future expenses?
Use what you expect to spend per year in retirement, in today's dollars. The calculator uses an inflation-adjusted (real) return, so the result is expressed in today's money too. Remember costs that may change, such as health insurance before Medicare, housing and travel.
What are Lean FIRE and Fat FIRE?
They're informal labels for the lifestyle your number supports. Lean FIRE targets a frugal budget (often under about $40,000 a year), while Fat FIRE targets a more generous one (often $100,000 or more). The math is the same: change the yearly expenses to see each target.
Does the calculator account for taxes?
Not directly. If you'll pay tax on withdrawals, include an estimate of those taxes in your yearly expenses so your FIRE number covers them.
Sources
- Determining Withdrawal Rates Using Historical Data (W. P. Bengen, 1994), Journal of Financial Planning, via the Financial Planning Association
- Consumer Price Index (CPI), U.S. Bureau of Labor Statistics
- Topic no. 557, Additional tax on early distributions from traditional and Roth IRAs, Internal Revenue Service
This calculator is for educational purposes and gives estimates based on the numbers you enter. It is not financial, tax or legal advice. Last reviewed October 2026.