How to Calculate Your FIRE Number (and What FU Money Actually Costs)
One division problem, four inputs, and the milestone most people hit long before full independence.
The Short Version
Your FIRE number is your expected annual retirement spending divided by your safe withdrawal rate.
At the standard 4% rate, that is the same as multiplying annual spending by 25. If you expect to spend $60,000 a year, your FIRE number is $60,000 ÷ 0.04 = $1,500,000.
Use 3.5% instead of 4% if you are planning a retirement longer than about 30 years — that raises the same target to roughly $1,714,000.
The division is the easy part. Nearly all of the difficulty in this calculation sits in the numerator: working out what you will actually spend once you stop working. This guide covers both, plus the two intermediate milestones — the crossover point and FU money — that arrive years before the full number and change your options immediately.
- FIRE number = annual spending ÷ withdrawal rate. Dividing by 4% and multiplying by 25 are the same operation.
- The withdrawal rate you choose should reflect your retirement length, not convention — 4% was researched for 30 years, not 50.
- Estimating spending is the hard part; the BLS Consumer Expenditure Survey gives a useful reality check against your own figures.
- The crossover point — when investment income exceeds expenses — is a milestone from Your Money or Your Life, and it arrives before your full number.
- FU money is partial independence: enough to walk away from a job without a plan. It typically costs a fraction of full FIRE.
Step 1: The Formula Itself
The reason 25 appears everywhere in FIRE writing is simply that 1 ÷ 0.04 = 25. It is not a separate rule. Change the withdrawal rate and the multiplier changes with it: 3.5% implies a multiplier of about 28.6, and 3% implies 33.3.
| Withdrawal rate | Multiplier | Target on $50,000/yr | Target on $80,000/yr | Typically used for |
|---|---|---|---|---|
| 5.0% | 20× | $1,000,000 | $1,600,000 | Aggressive; short horizons or with other income sources |
| 4.0% | 25× | $1,250,000 | $2,000,000 | The standard; researched against ~30-year retirements |
| 3.5% | 28.6× | $1,428,571 | $2,285,714 | Retirements of 40+ years |
| 3.0% | 33.3× | $1,666,667 | $2,666,667 | Very long horizons or low risk tolerance |
The 4% convention comes from William Bengen's 1994 analysis of historical withdrawal rates and the 1998 Trinity Study by Cooley, Hubbard and Walz, both of which tested 30-year retirement periods against historical US market data. Someone retiring at 40 is planning for a period substantially longer than either study modelled, which is the entire argument for the more conservative rates in the table.
Step 2: The Hard Part — Estimating Your Spending
A 10% error in your spending estimate becomes a 10% error in your target — $150,000 on a $1.5 million number. This step deserves more time than the arithmetic.
Start with twelve months of real transactions. Not a budget, not an estimate — actual bank and card records for a full year, which captures annual and irregular costs like insurance premiums, car registration, holidays and medical bills that a single month misses entirely.
Then adjust for what genuinely changes when you stop working:
| Category | Direction in retirement | Notes |
|---|---|---|
| Payroll taxes | Falls sharply | Social Security and Medicare taxes apply to earned income, not portfolio withdrawals |
| Commuting and work costs | Falls | Transport, work clothing, lunches, professional dues |
| Retirement contributions | Stops | You are spending the portfolio now, not funding it — often a large line |
| Mortgage | May stop entirely | Only if paid off; a remaining balance changes the number materially |
| Health insurance | Rises, often steeply | Employer coverage ends; you fund it yourself until Medicare at 65 |
| Travel and hobbies | Usually rises | More free time generally means more discretionary spending, especially early on |
For a sanity check against national data: the Bureau of Labor Statistics Consumer Expenditure Survey reports that US households with a reference person aged 65 or older spent an average of $61,432 in 2024, while households aged 65–74 — closer to the early-retirement profile — spent $65,354. Average spending across all US households was $78,535, and average healthcare spending was $6,197.
If your own estimate lands far below this, confirm you have accounted for healthcare and irregular costs. If it lands far above, confirm the excess is discretionary spending you could cut in a bad market rather than fixed obligations.
Enter your spending estimate, current savings, annual contributions and withdrawal rate to see your number and timeline.
Calculate your FIRE numberStep 3: Worked Examples
Three complete calculations, each showing the target and the years required. All assume a 7% real return with contributions added at the end of each year — the same mechanics the calculator uses, and all figures verified against it.
Example 1 — Mid-career, moderate spending
Annual spending $60,000. Current invested savings $50,000. Saving $30,000 per year. Withdrawal rate 4%.
- FIRE number: $60,000 ÷ 0.04 = $1,500,000
- Years to financial independence: 21 years
- First-year withdrawal at target: $60,000
Example 2 — Early start, lean target
Annual spending $40,000. Starting from $0. Saving $20,000 per year. Withdrawal rate 4%.
- FIRE number: $40,000 ÷ 0.04 = $1,000,000
- Years to financial independence: 23 years
Example 3 — The same plan, run conservatively
Identical to Example 1 — $60,000 spending, $50,000 saved, $30,000 per year — but using a 3.5% withdrawal rate for a longer retirement.
- FIRE number: $60,000 ÷ 0.035 = $1,714,286
- Years to financial independence: 23 years
The Crossover Point: The Milestone Before the Finish Line
The crossover point is the moment your monthly investment income exceeds your monthly expenses. The concept comes from Your Money or Your Life by Vicki Robin and Joe Dominguez, which asked readers to chart both lines on the same graph each month and watch for the intersection.
"The crossover point is where the two lines meet: the month your investments earn more than you spend."
— The framework popularised by Your Money or Your Life
Mathematically the crossover point and the FIRE number describe the same threshold — if your portfolio generates more than you spend at your chosen withdrawal rate, you have reached your number. The value of the crossover framing is psychological rather than mathematical. Watching two lines converge month by month makes an abstract, decades-away target feel like measurable progress, and it makes the effect of every additional contribution visible.
It also reframes the goal usefully. Cutting $500 a month from your spending does not just free up $500 to invest — it lowers the line you are trying to cross, pulling the intersection nearer from both directions at once. At a 4% withdrawal rate, permanently removing $500 a month of spending reduces your FIRE number by $150,000.
Track the invested assets that generate the income side of your crossover chart.
Track your net worthFU Money: Partial Independence, and What It Costs
FU money is the amount that lets you walk away from a job, a client or a situation without a plan lined up. It is not retirement. It is leverage — the ability to say no without immediate financial consequence.
There is no formula for it in the way there is for the FIRE number, because it describes a threshold of personal comfort rather than a permanent withdrawal. Three ways people commonly frame it:
| Framing | Typical size | What it buys |
|---|---|---|
| Runway FU money | 1–3 years of expenses | Quit without another job. On $50,000 of annual spending: $50,000–$150,000 |
| Partial FI | 25–50% of your FIRE number | Portfolio covers a meaningful share of expenses; work becomes optional in kind, not amount |
| Coast FIRE | Varies by age and target | Retirement fully funded by compounding alone; current income only needs to cover current life |
The runway framing is the most concrete and the most commonly meant. Note that it is fundamentally different arithmetic from the FIRE number: runway money is designed to be spent down over a defined period, while the FIRE number is designed to be spent from indefinitely. A three-year runway is a bridge, not an endowment.
Coast FIRE is the most mathematically interesting of the three, because it is the point where the compounding does the remaining work for you and retirement saving can stop entirely.
Find the balance at which compound growth alone reaches your full FIRE number by your target age.
Calculate your Coast FIRE numberWhat Actually Moves Your Number
Four inputs drive the result. Ranked by how much leverage each one gives you:
- Annual spending. The highest-leverage input by a wide margin, because it works on both sides of the equation — every dollar of permanent spending reduction lowers the target by 25 dollars at a 4% rate and frees a dollar to invest.
- Savings rate. Governs the timeline more than the target. The share of income you keep is what determines the years, not the absolute size of your number.
- Withdrawal rate. Sets how conservative the plan is. Moving from 4% to 3.5% raises the target about 14% and buys meaningful margin against long retirements.
- Expected return. The input you control least. A 7% real return reflects long-run historical equity performance, but the sequence of returns — the order good and bad years arrive — matters as much as the average, especially early in retirement.
For the surrounding framework — variant definitions, healthcare, tax placement and withdrawal sequencing — see The FIRE Roadmap. For a comparison of the spending tiers and what each portfolio target implies, see Lean vs Chubby vs Fat FIRE. For the research behind the withdrawal rate itself, see Safe Withdrawal Rate Explained.
Your number, your years to independence, and your first-year withdrawal — from your own inputs.
Run your numbers- 1Determining Withdrawal Rates Using Historical Data — William P. Bengen, Journal of Financial Planning, 1994
- 2Portfolio Success Rates: Where to Draw the Line (Trinity Study, updated) — Cooley, Hubbard & Walz, Journal of Financial Planning, 2011
- 3Consumer Expenditure Surveys — 2024 Results — U.S. Bureau of Labor Statistics, 2024 data
- 4Total Average Annual Expenditures by Age: 65 to 74 — BLS via FRED, Federal Reserve Bank of St. Louis, 2024
- 5Compound Interest Calculator — U.S. Securities and Exchange Commission, Investor.gov
- 6Health Coverage Options If You Retire Before 65 — HealthCare.gov, Centers for Medicare & Medicaid Services
- 7Retirement Plans: Contribution Limits — Internal Revenue Service
A research-first finance team. No lead selling, no lender rankings, no affiliate-pulled recommendations. Every guide pairs primary sources (IRS, CFPB, Federal Reserve, CRA) with the free calculators you can run yourself.
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Frequently asked questions
Keep reading
The FIRE Roadmap: Retire Early by the Numbers (2026 Edition)
The FIRE movement in plain math: 25x rule, 4% safe withdrawal, Coast and Fat FIRE numbers, healthcare gaps, and the tax moves that make early retirement work.
Read guideLean FIRE vs Chubby FIRE vs Fat FIRE: The Actual Numbers
Lean, Chubby, Fat and Barista FIRE compared with real portfolio targets at 4% and 3.5% withdrawal rates — plus why none of these labels has an official definition.
Read guideHow to Estimate Retirement Expenses (Full Category Checklist)
A complete retirement expense checklist with real BLS spending data by category, the costs people forget, and how your estimate sets your FIRE number.
Read guideSafe Withdrawal Rate Explained: The Math Behind the 4% Rule (2026)
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