Your FIRE number is the size of the invested portfolio that can fund your life indefinitely, and the fastest way to find it is to multiply your annual spending by 25 (a 4% safe withdrawal rate) or by 33 if you want the more conservative 3% rate. If you spend $40,000 a year, your FIRE number is roughly $1,000,000 at 4% or $1,333,333 at 3%. That single target is what separates financial independence from ordinary retirement planning: you are not aiming for an age, you are aiming for a multiple of your own expenses. This guide shows you exactly how to calculate that multiple, why the withdrawal rate you pick changes the answer so much, and the two costs - taxes and pre-Medicare healthcare - that quietly push the real number higher. Run your own figures any time in the free FIRE calculator.
One framing point before the math. A traditional plan starts with an age and works backward; a FIRE plan starts with a spending number and works backward to a portfolio. That is why the FIRE calculator asks for annual expenses, not a retirement age, and why your spending - not your salary - is the input that decides everything.
The core formula: spending divided by your withdrawal rate
Your FIRE number equals annual spending divided by your safe withdrawal rate (SWR). Because dividing by 4% is the same as multiplying by 25, the rule of thumb you will see everywhere is 25x annual expenses.
FIRE number = annual spending / SWR = annual spending x (1 / SWR)
The withdrawal rate is the slice of your portfolio you plan to live on each year, adjusted upward for inflation annually. The famous 4% figure comes from the Trinity study and William Bengen's research on historical US market data, which found that a portfolio withdrawing 4% in year one (then raising that dollar amount with inflation) survived most 30-year retirement windows. Early retirees often plan for 40 to 60 years, not 30, so many choose a lower rate - 3% to 3.5% - which raises the multiple. Here is how the multiple changes with the rate:
| Safe withdrawal rate | Multiple of spending | FIRE number for $40,000/yr |
|---|---|---|
| 4.0% | 25x | $1,000,000 |
| 3.5% | 28.6x | $1,142,857 |
| 3.0% | 33.3x | $1,333,333 |
Dropping from 4% to 3% adds a third to your target. That is not a rounding error - it can mean several extra years of work. The trade is real: a lower rate buys a wider safety margin against bad early markets, while a higher rate gets you out sooner but with less cushion.
FIRE number by spending level
Because the formula is just spending times a multiple, your number scales directly with your lifestyle. The table below shows the target at each of the three common withdrawal rates so you can find the row closest to your annual budget. Every figure is annual spending divided by the rate.
| Annual spending | At 4% (25x) | At 3.5% (28.6x) | At 3% (33.3x) |
|---|---|---|---|
| $30,000 | $750,000 | $857,143 | $1,000,000 |
| $40,000 | $1,000,000 | $1,142,857 | $1,333,333 |
| $50,000 | $1,250,000 | $1,428,571 | $1,666,667 |
| $60,000 | $1,500,000 | $1,714,286 | $2,000,000 |
| $80,000 | $2,000,000 | $2,285,714 | $2,666,667 |
| $100,000 | $2,500,000 | $2,857,143 | $3,333,333 |
The most useful insight in this table is hidden in the left column: cutting $10,000 off your annual spending lowers your 4% target by $250,000. Every recurring expense you eliminate is worth 25 times its annual cost in portfolio you no longer have to build. That is why FIRE planners track spending obsessively - it is the only input that works on both sides of the equation at once.
The number on the calculator is not the number you need to budget
The 25x figure assumes the dollars you withdraw equal the dollars you can spend. In real life, two costs sit between your withdrawal and your grocery bill, and both raise the true target: taxes and healthcare before Medicare. The fix is to gross up your spending before you apply the multiple.
Gross up for taxes
Withdrawals from a traditional 401(k) or IRA are taxed as ordinary income, and even brokerage withdrawals can trigger capital-gains tax. If you need $40,000 of cash and expect to lose 10% to taxes, you must withdraw $40,000 / (1 - 0.10) = $44,444, which raises your 4% FIRE number from $1,000,000 to about $1,111,111. The exact rate depends on your account mix and state, so treat 10% as an illustration, not a promise - early retirees with mostly Roth and taxable money often pay far less.
Add the healthcare gap before age 65
Medicare does not start until 65, so a 45-year-old retiree faces roughly 20 years of buying their own coverage. If you budget, say, $12,000 a year for an ACA marketplace plan and out-of-pocket costs, that goes straight into your spending number before you multiply. Here is the combined effect on a $40,000 baseline:
| Scenario | Gross annual need | FIRE number at 4% |
|---|---|---|
| Bare spending only | $40,000 | $1,000,000 |
| + $12,000 healthcare | $52,000 | $1,300,000 |
| + healthcare + 10% tax gross-up | $57,778 | $1,444,444 |
The honest FIRE number for this household is closer to $1.44 million than the headline $1 million. None of this means FIRE is unrealistic - it means the simple 25x figure is a floor, not a finished plan. Estimate your own after-tax cash flow with the take-home pay calculator and your draw-down with the retirement withdrawal calculator.
Why your withdrawals are inflation-adjusted (and your target should be too)
The 4% rule assumes you raise your withdrawal each year to keep pace with rising prices, so your spending power stays flat even as the dollar shrinks. That has two consequences. First, you should use a real (after-inflation) return - around 5% rather than a nominal 7% to 8% - when projecting how long it takes to reach the number, so inflation is already baked in. Second, your FIRE number itself should be stated in today's dollars; if you plan to retire in 15 years, the same lifestyle will cost more nominal dollars then, so re-run the math in real terms. The inflation calculator shows how much a fixed budget erodes over time, and the compound interest calculator lets you test real versus nominal growth side by side.
How to calculate your own FIRE number
You can get a defensible number in a few minutes. Here is the order that keeps you from under-counting.
- Total your real annual spending. Use 12 months of actual outflows, not an optimistic budget. Include housing, food, transport, insurance, and the occasional big-ticket items most people forget.
- Add the costs that hit only in early retirement. Layer in pre-Medicare health coverage and any expenses your job currently covers, like employer health premiums.
- Gross up for taxes. Divide your cash need by (1 minus your expected effective tax rate) to get the amount you must actually withdraw.
- Pick your withdrawal rate. Use 4% for a roughly 30-year horizon, or 3% to 3.5% if you are retiring young and want a wider margin.
- Divide spending by the rate. Grossed-up annual spending / SWR is your FIRE number. Enter your figures in the FIRE calculator to confirm it and see how many years your current savings rate needs.
FIRE number vs a retirement nest egg: the key difference
A standard retirement target is usually framed as a percentage of your income replaced at a fixed age. A FIRE number is framed as a multiple of your spending with no age attached. The distinction matters because two people earning the same salary can have wildly different FIRE numbers if one spends $40,000 and the other spends $80,000 - the lower spender needs half the portfolio and can stop working years sooner. If you want the age-and-income version, use the retirement calculator; for the savings-vehicle side, the Roth IRA calculator and 401(k) calculator show how tax-advantaged accounts build that portfolio faster. For broad context on the 4% guideline and historical withdrawal research, the U.S. Securities and Exchange Commission (Investor.gov) publishes plain-language investing resources.
The bottom line
Your FIRE number is annual spending times 25 at a 4% withdrawal rate, or times 33 at 3% - but the figure you can trust is the one you build from real spending, grossed up for taxes and pre-Medicare healthcare. For a $40,000 lifestyle that pushes the honest target from a tidy $1,000,000 toward roughly $1.44 million once those costs are in. The lever that moves it most is your spending: every $10,000 you trim cuts $250,000 off the goal. Calculate your spending carefully, choose a withdrawal rate that matches how long you will be retired, then run it through the FIRE calculator to see both your number and your timeline. Explore more tools in the retirement hub or head back to the homepage for the full toolkit.
Try it yourself
Run your own numbers in the free FIRE Calculator — instant, private, no sign-up.
Open the FIRE Calculator →Frequently asked questions
- What is my FIRE number?
- Your FIRE number is your annual spending divided by your safe withdrawal rate. At a 4% rate that is 25 times your spending, so a $40,000-a-year lifestyle needs about $1,000,000; at a more conservative 3% rate the multiple rises to about 33x, or $1,333,333. Use your real spending, not your income, because spending is the only input that sets the target.
- How do I calculate my FIRE number with the 4% rule?
- Divide your annual spending by 0.04, which is the same as multiplying by 25. For example, $50,000 of annual spending divided by 0.04 equals $1,250,000, and $30,000 divided by 0.04 equals $750,000. The 4% rule assumes you withdraw 4% in year one and raise that dollar amount with inflation each year afterward.
- Should I use a 4% or 3% withdrawal rate?
- Use 4% if you expect a roughly 30-year retirement and 3% to 3.5% if you are retiring young and want a wider safety margin. The choice matters a lot: at $40,000 of spending, 4% targets $1,000,000 while 3% targets $1,333,333, a third more portfolio and often several extra years of saving. A lower rate trades a later finish line for more protection against weak early markets.
- Does my FIRE number include taxes and healthcare?
- No, the basic 25x figure does not, and ignoring them understates your true target. Gross up your spending first: add a pre-Medicare healthcare budget (a $40,000 lifestyle plus $12,000 of coverage becomes $52,000, or $1,300,000 at 4%), then divide by one minus your expected tax rate. After a 10% tax gross-up that example rises to about $57,778 a year, or roughly $1,444,444.
- Why does cutting spending lower my FIRE number so much?
- Because every dollar of annual spending is multiplied by 25 at a 4% rate, so cutting $10,000 a year lowers your target by $250,000. Spending is the rare lever that works on both sides of the plan at once: a lower budget shrinks the number you need and frees up more money to invest toward it. That is why FIRE planners track expenses so closely.
- Is the FIRE number in today's dollars or future dollars?
- State your FIRE number in today's dollars and plan with a real, after-inflation return of around 5% rather than a nominal 7% to 8%. The 4% rule already assumes you raise withdrawals with inflation each year, so using a real return keeps the target and the timeline consistent. Re-check the figure as your spending changes, since the target moves with your lifestyle, not the calendar.
Related guides
401(k) Employer Match Explained: The Free Money Most Workers Leave on the Table · What to Do With an Old 401(k): Your Four Options and the Real Cost of Each · Coast FIRE: How Much You Need So You Can Stop Saving · How Much Money Do I Need to Retire?