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FIRE Calculator

Enter your age, annual expenses, savings and yearly contributions to project when your investments reach financial independence using the 4% rule or a custom withdrawal rate, all computed locally in your browser.

FIRE — financial independence, retire early — comes down to a sum of money large enough to work in your place: invest it, withdraw a small share each year to cover the bills, and the rest keeps growing. How large? Annual spending divided by a safe withdrawal rate — under the classic 4% rule, spending × 25, so 40,000 a year needs a million. The figure sounds daunting until it is broken into how much to save and how many years it takes.

Inflation is the part most often left out: today's million is not a million in ten years, and a target that does not rise with prices produces a retirement age that is too optimistic. This tool simulates year by year at a nominal return with the target indexed to inflation, and shows both the nominal balance and its value in today's money in the trajectory table, so the two views can be compared.

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How to use

  1. Enter your age, annual spending, investable savings and the amount added each year.
  2. Set the safe withdrawal rate, the expected return and the inflation rate.
  3. Read the FIRE number and the projected retirement age.
  4. Use the trajectory table to compare the nominal balance with its value in today's money.

How it works

How the FIRE principal is computed

FIRE principal = annual spending / safe withdrawal rate, which at 4% is annual spending x 25. The logic: the principal grows at long-term returns, you withdraw 4% yearly for spending, and the principal still beats inflation, so the money likely lasts forever; the more conservative the rate, the larger the principal needed.

Why the withdrawal rate is often 4%

The 4% comes from research on historical stock-bond portfolio drawdowns: a portfolio withdrawing 4% doesn't run out in the vast majority of 30-year cycles. It's not a guarantee — an early severe bear market remains dangerous — so some use a more conservative 3-3.5%, at the cost of a 20-30% higher principal threshold.

What the two trajectory values mean

The nominal value is the money on the books that year; purchasing-power discounting divides it by cumulative inflation to convert it back into "today's money." The target line rising with inflation is the nominal convention, while your sense of living standard is the purchasing-power convention — comparing the two avoids the illusion of "doubled on paper, no real gain."

What the model doesn't consider

The model assumes a constant annual return, excluding taxes, return volatility and contribution gaps from unemployment; post-retirement cash flow is also simplified to the same withdrawal rate. It's good for directional judgment — three years short or ten, how many years earlier from saving one more year — but month-precise planning belongs to a professional financial advisor.

Code example

JavaScript The FIRE number: annual spending over the withdrawal rate 

// The 4% rule: 25x annual spending, i.e. / 4%
const fireNow = 120000 / 0.04;   // 3,000,000

// Inflation cannot be ignored: raise the target by annual inflation
const target = fireNow * Math.pow(1.03, 10);   // ≈ 4,030,000 (after 10 years)

JavaScript Year by year: compounding balance, rising target 

balance = balance * (1 + rate) + annualSaving;   // nominal return compounding + yearly addition
const targetN = fireNow * Math.pow(1 + infl, n); // the year-n target (raised with inflation)

// The first year where balance >= target is the retirement year
// The display also gives today's purchasing power: balance / (1+infl)^n

FAQ

What annual spending should I enter for FIRE?

Enter the annual spending of the living standard you want after retirement, not the number you squeeze out now by scrimping. Include the post-payoff figure if you have a mortgage, and factor in the education phase if you have children — setting the target too low makes the retirement age it computes lie to you.

Does the 4% rule apply in China?

The 4% comes from US stock history; A-shares are more volatile with lower risk-free rates, so copying it directly is aggressive. A steadier approach is lowering to 3-3.5%, or executing "4% withdrawal + a two-year cash pool"; this tool supports a custom rate.

Why does my projection never reach the goal by the age cap?

Most likely annual spending is too high relative to savings, or the return assumption too low. FIRE principal is proportional to annual spending — cutting spending 20% lowers the threshold 20%; look at how fast the gap in the trajectory table narrows, then decide whether to retire later or save more.

Why does the trajectory table show only milestone years?

Listing every year would produce dozens of rows, and early-year numbers change little. Keeping a row every 5 years, the goal year and the last year is enough to see the shape of the compounding curve; to see it yearly, lower the age cap for denser sampling.

What if the initial savings already reach the FIRE principal?

The result shows "already reached now" — a hint that at your current spending you can stop anytime. Note that the retirement age then equals the current age, meaning the longest number of years to support, so consider adjusting the withdrawal rate to a more conservative tier and rechecking.

Does the calculation need a connection? Is data uploaded?

No connection needed; input is used only locally in the browser, not stored or uploaded. On another device just re-enter — no account or sync.

How is a mid-way gap from unemployment handled?

The current version simplifies as "savings invested evenly each year" and doesn't support interruptions. A rough fix: record zero savings for the gap years and make up the corresponding shortfall, or spread annual savings over the whole period and recompute — the result is slightly conservative.