How to use the FIRE calculator
Start with the figures you already track. The calculator turns Annual spending ($) and Safe withdrawal rate (%) into a FIRE number, then projects your balance using Current invested savings ($), Annual contribution to savings ($) (required; enter 0 if none), and Expected annual investment return (%). It also shows the amount still needed and the estimated FI year.
- Enter Current invested savings ($), Annual spending ($), Annual contribution to savings ($) (required; enter 0 if none), Expected annual investment return (%), and Safe withdrawal rate (%).
- Enter Current age (optional) to add Estimated FI age to the result.
- Click Calculate. The page checks the fields and displays the FIRE number, projection, and assumptions.
- Click Copy result for the plain-text summary, or click Download result (.txt) to save a text file.
How the FIRE number is calculated
The FIRE number is Annual spending ($) divided by Safe withdrawal rate (%), converted to a decimal. For example:
Annual spending: $40,000
Safe withdrawal rate: 4%
FIRE number (target): $1,000,000Amount still needed is the FIRE number minus Current invested savings ($), with zero as the lowest value. Each projected year applies Expected annual investment return (%) to the balance, then adds Annual contribution to savings ($) (required; enter 0 if none) at year end.
How the calculator estimates your FI year
The calculator checks the balance after each simulated year. The first year that reaches or exceeds the FIRE number becomes Years to FI. Estimated FI year adds that value to the current calendar year from the browser, and Estimated FI age adds it to Current age (optional) when an age was entered.
When Current invested savings ($) already reaches the target, Years to FI shows Already reached, uses zero years, and the schedule stays hidden. Otherwise, the simulation runs for up to 100 years. The displayed schedule has Calendar year, Years from now, and Projected balance, with at most 40 simulated years.
What the FIRE calculator leaves unchanged
The calculation uses Annual spending ($), Annual contribution to savings ($) (required; enter 0 if none), and Expected annual investment return (%) exactly as entered. It does not adjust for inflation or calculate taxes. It also does not model market volatility, sequence-of-return risk, Social Security, or other future income.
Current invested savings ($) and Annual contribution to savings ($) (required; enter 0 if none) allow 0 to 1e12. Annual spending ($) must be greater than 0 and no more than 1e12. Expected annual investment return (%) accepts 0% to 30%, Safe withdrawal rate (%) accepts 0.1% to 20%, and Current age (optional) accepts 10 to 100.
When to use the FIRE calculator
Enter a proposed spending level and savings contribution to see how the target date changes before you revise a plan. Test another Safe withdrawal rate (%) to see its direct effect on the FIRE number and Amount still needed.
The script processes the fields in the browser. It does not upload or fetch the values, and the projection does not provide personalized financial advice.
Choose the right financial calculator
Use the Financial Calculators category for another money model. The Compound Interest Calculator covers growth from principal, rate, term, and compounding frequency. The Emergency Fund Calculator builds a target from monthly expenses, income stability, and target months. The Retirement Income Calculator estimates sustainable annual retirement income from savings, contributions, retirement age, spending, return, and inflation.
Frequently asked questions
How do I calculate my FIRE number?
Divide Annual spending ($) by Safe withdrawal rate (%) expressed as a decimal. The calculator then subtracts Current invested savings ($) to show Amount still needed, with zero as the floor.
What does the FIRE calculator use for annual growth?
It compounds the balance once each year using Expected annual investment return (%), then adds Annual contribution to savings ($) (required; enter 0 if none) at year end.
How does the calculator estimate the FI year?
It finds the first simulated year in which Projected balance reaches or exceeds the FIRE number, then adds that number of years to the current calendar year from the browser.
Does the FIRE calculator adjust for inflation?
The calculator uses Annual spending ($), Annual contribution to savings ($) (required; enter 0 if none), and Expected annual investment return (%) exactly as entered. It applies no automatic inflation adjustment.
What happens if my FIRE target is not reached?
Years to FI says "Not reached within 100 years" when the balance stays below the target through the simulation limit. The visible schedule contains at most the first 40 simulated years.