How this calculator works
FIRE stands for Financial Independence, Retire Early. A 'FIRE number' is the invested portfolio size that, according to a chosen safe withdrawal rate, can cover your annual spending indefinitely without running out — so reaching it means your investments alone could theoretically support you.
This calculator computes that number from your annual expenses and withdrawal rate, then simulates month by month how long it will take your current savings and ongoing contributions to reach it at your expected investment return. It also reports a coast FIRE estimate: how long your current savings alone, with no further contributions, would take to reach the same number purely through compounding.
The formulas
FIRE number = annual expenses ÷ safe withdrawal rate (as a decimal)Equivalently, FIRE number = annual expenses × 25 when the withdrawal rate is 4%, since 1 ÷ 0.04 = 25Years to reach it: simulated month by month with your savings compounding at the expected return, until the balance reaches the FIRE numberCoast FIRE: the same simulation, but with monthly contributions set to zero — current savings compounding aloneThe 4% figure is often called the Trinity-study heuristic, after a 1998 academic paper analyzing historical U.S. market data. It is a widely used planning guideline, not a guarantee for any specific future retirement — a lower withdrawal rate (say 3% to 3.5%) is more conservative for a longer retirement horizon.
Worked example: $40,000 annual expenses, 4% withdrawal rate
- FIRE number = 40,000 ÷ 0.04 = $1,000,000 (equivalently, 40,000 × 25).
- Starting from $50,000 saved, adding $20,000 a year ($1,667/month), at a 7% expected annual return, the simulation reaches $1,000,000 in about 19 years and 3 months.
- Coast FIRE check: if contributions stopped today, the same $50,000 alone, left to compound at 7%, is projected to reach $1,000,000 in about 43 years — much longer than with ongoing contributions, showing how much continued saving accelerates the timeline.
Frequently asked questions
Why 4%? Could I use a different withdrawal rate?
4% comes from historical simulations (often called Trinity-style studies) of how a diversified stock-and-bond portfolio would have survived a 30-year retirement under a fixed withdrawal rate. Many FIRE planners use a more conservative 3% to 3.5% for retirements expected to last longer than 30 years. Enter whichever rate matches your own risk tolerance and time horizon — the calculator recomputes the FIRE number instantly.
What is coast FIRE?
Coast FIRE is the point at which your current savings, left completely untouched, are projected to grow to your full FIRE number by compounding alone — meaning you could stop contributing and still reach financial independence eventually, though you would still need to cover living expenses from current income until then.
Does the FIRE number include Social Security or a pension?
No. This calculator projects only your entered savings and contributions growing at your expected return. Any other future income (Social Security, a pension, rental income) would let you reach the same lifestyle with a smaller invested portfolio than the FIRE number alone suggests.
Is a 7% expected return realistic?
It is a commonly used planning assumption for a diversified stock-heavy portfolio over long periods, but actual returns vary significantly year to year and are not guaranteed. Running the calculator at a lower return (5-6%) alongside your main estimate gives a sense of how sensitive your timeline is to market performance.
How much faster do I reach my FIRE number by contributing more each month?
Contributing more each month shortens the years-to-reach simulation, since the calculator adds your monthly contribution to a compounding balance every month until it reaches the FIRE number — more added each month means the target is reached sooner, all else equal. In the worked example, contributing $20,000 a year ($1,667/month) toward a $1,000,000 target at a 7% return reaches it in about 19 years and 3 months; a larger monthly contribution toward that same target would reach it in fewer years, though the exact time depends on running the simulation with the new amount.