FIRE Number Calculator

How to Use the FIRE Number Calculator

The FIRE number calculator turns a retirement goal into a concrete portfolio target. Start with the annual spending you want your investments to cover in today's dollars, then choose a withdrawal rate that matches the length and flexibility of your retirement. A traditional thirty-year retirement often starts with the 4% rule as a benchmark. An early retirement that may last forty, fifty, or sixty years usually deserves a more conservative starting point, such as 3% to 3.5%, unless you have major flexible spending, pension income, or other safety margins.

Your current portfolio and annual contributions do not change the FIRE number itself. They change the projected timeline. The target is driven by spending and withdrawal rate; the years-to-FIRE estimate is driven by current savings, future contributions, inflation, and investment return assumptions. Treat the output as a planning range, not a promise. A good plan reruns the calculation whenever your rent, mortgage, healthcare costs, family size, or tax picture changes.

Inputs that matter most

• Annual expenses: Include the spending that investments must fund, not every dollar that moves through your accounts.
• Withdrawal rate: Lower rates require a larger portfolio but leave more room for long retirements and bad markets.
• Current portfolio: Use investable assets, not emergency cash, home equity, or money already earmarked for near-term spending.
• Annual contributions: Include recurring retirement-account and taxable brokerage investments you expect to sustain.
• Return and inflation: The calculator converts nominal returns into a real return so the target stays in today's purchasing power.

FIRE Number Formula

The core formula is simple: annual expenses ÷ withdrawal rate = FIRE number. If you spend $60,000 per year and use a 4% withdrawal rate, the target is $1,500,000. If you use 3.5%, the target rises to about $1,714,286. If you use 3%, the target becomes $2,000,000. The math is intentionally transparent because the assumption matters more than the calculator interface.

The 4% rule is often associated with William Bengen's research and the Trinity Study. Those studies are useful starting points, but they were built around historical market data and retirement horizons that may not match a thirty-five-year-old early retiree. A longer horizon means more time for sequence risk, valuation risk, inflation surprises, tax-law changes, and spending shocks to appear. That is why this page links the FIRE target to the safe withdrawal rate calculator: the target tells you how much you need; the withdrawal tool stress-tests how robust that target may be.

A practical way to use the formula is to run three scenarios. First, calculate your baseline target from current spending. Second, run a leaner target that removes temporary or discretionary expenses. Third, run a comfort target that includes healthcare, travel, housing repairs, children, family support, or other spending that may be easy to underestimate. The spread between those three targets is often more useful than a single exact number.

Common FIRE Number Mistakes

• Using gross income instead of expenses. FIRE is funded by spending needs, not salary.
• Ignoring taxes. A taxable withdrawal, Roth withdrawal, and HSA reimbursement do not have the same after-tax value.
• Assuming 4% is always safe. The historical 4% rule is not a guarantee, especially for 40+ year retirements.
• Counting home equity twice. Home equity can reduce housing costs, but it is not spendable portfolio value unless you plan to sell, borrow, or downsize.
• Forgetting healthcare and insurance. Early retirees may face ACA subsidy cliffs, private insurance costs, or long-term-care risk.
• Stopping at the target number. Use the Coast FIRE calculator to understand savings pressure and the sequence-risk tools to test bad timing.