Your FIRE number is the single most important figure in the financial independence movement: the portfolio size at which work becomes optional. Below it, you work because you have to. Above it, your investments can fund your life indefinitely — and every hour you work after that is a choice. This guide shows you exactly how to calculate yours, how it changes across the four flavors of FIRE, and how your savings rate controls the date you’ll arrive.
The Formula
The FIRE number comes straight from the 4% rule — the research-backed finding that a diversified portfolio historically sustained ~4% annual inflation-adjusted withdrawals for 30+ years:
FIRE Number = Annual Retirement Spending × 25
(Equivalently: spending ÷ safe withdrawal rate. At 4%, dividing by 0.04 is the same as multiplying by 25.)
Worked example. Meet Casey, who expects to spend $48,000/year in retirement:
FIRE Number = $48,000 ÷ 0.04 = $1,200,000
At $1.2M invested, Casey’s portfolio can fund $48,000 in year one, adjusted upward for inflation every year after. If Casey expects $20,000/year from Social Security, the portfolio only needs to cover the $28,000 gap — dropping the FIRE number to $700,000. Guaranteed income always gets subtracted first; see Coast FIRE with Social Security for the full method.
FIRE Numbers for the Four Flavors of FIRE
“FIRE” isn’t one target — it’s a family of strategies, and each has its own number:
| Type | Spending profile | How the number is set | Example FIRE number |
|---|---|---|---|
| Lean FIRE | Frugal, under ~$40k/yr | Spending × 25 | $25k spending → $625,000 |
| Coast FIRE | Any | Amount needed today that grows to full FIRE number by retirement | $319k at 30 (coasts to $1M at 60) |
| Barista FIRE | Any + part-time work | (Spending − part-time income) × 25 | $50k spending, $20k income → $750,000 |
| Fat FIRE | Luxurious, $100k+/yr | Spending × 25 | $100k spending → $2,500,000 |
A few notes on each:
- Lean FIRE proves the target is a choice: a $25,000 lifestyle needs $625,000, reachable on ordinary incomes with a high savings rate — at the price of permanent frugality.
- Coast FIRE is structurally different: it’s not a retirement-day number but a today number. You’re done saving once your investments can grow to the full FIRE number on their own. The full definition lives in our What is Coast FIRE? guide, and the math in the Coast FIRE formula breakdown.
- Barista FIRE shrinks the portfolio by replacing withdrawals with part-time paychecks. Cover $20,000/year of a $50,000 budget with work, and the portfolio requirement falls from $1,250,000 to $750,000. Trade-offs in Coast FIRE vs Barista FIRE.
- Fat FIRE is the same multiplication with a bigger input: $100,000/year requires $2,500,000.
Your Savings Rate Sets Your Arrival Date
Here’s the most motivating math in the entire movement. Your savings rate works twice: it builds the portfolio faster and — because you’re living on the remainder — it lowers your FIRE number at the same time.
Assumptions for the table below: start from $0, invest at a 5% real (inflation-adjusted) return, and reach 25× your annual spending:
| Savings rate (% of income) | Spending rate | Years to FIRE |
|---|---|---|
| 20% | 80% | ~37 years |
| 25% | 75% | ~32 years |
| 30% | 70% | ~28 years |
| 40% | 60% | ~22 years |
| 50% | 50% | ~17 years |
Notice the shape: going from 20% to 30% saves ~9 years, but 40% to 50% saves only ~5. The early increases buy the most freedom. (These figures assume constant returns and a 4% withdrawal rate — real life adds volatility, taxes, and salary growth, so treat them as directional, not prophetic.)
There’s also a hidden nuance in the table: it assumes your retirement spending equals your current spending. If you save 30% now but plan to spend more freely in retirement, your timeline stretches accordingly.
Worked Example: From FIRE Number to Plan
Let’s put the whole thing together for one person. Meet Morgan:
- Age 35, earns $95,000, currently invests $120,000
- Spends $55,000/year now, expects $50,000/year in retirement (mortgage gone)
- Expects about $22,000/year from Social Security at full retirement age
- Assumptions: 7% nominal returns, 3% inflation (3.88% real), 4% withdrawal rate, retire at 65
Step 1 — portfolio-funded spending: $50,000 − $22,000 = $28,000/year
Step 2 — FIRE number: $28,000 × 25 = $700,000 (needed at 65)
Step 3 — Coast FIRE number today: $700,000 ÷ 1.0388^30 = $700,000 ÷ 3.1361 ≈ $223,204
Step 4 — the verdict: Morgan has $120,000 against a coast target of ~$223,204 — about 54% of the way to Coast FIRE, with 30 years of compounding still ahead. Continued contributions will cross the coast line well before 50, after which saving becomes optional.
Three lessons hide in that example: guaranteed income cut the FIRE number from $1,250,000 to $700,000; the coast target is a fraction of the retirement-day target; and a “modest” current balance can be much further along than it feels. (Note: Social Security starts at 67 while Morgan retires at 65, so a precise plan adds a small bridge fund for those two years — details in Coast FIRE with Social Security.)
Common Mistakes When Setting Your FIRE Number
- Using gross income instead of spending. Your number is built on what you’ll spend, not what you earn. Conflating the two can inflate the target by hundreds of thousands of dollars.
- Ignoring guaranteed income. Subtract Social Security and pensions before multiplying — every $1,000/year of guaranteed income removes $25,000 from your FIRE number.
- Forgetting inflation works both ways. If you set a spending target in today’s dollars, your return assumptions must be real (inflation-adjusted) or the target must be inflated. Mixing the two is the classic spreadsheet bug — our Coast FIRE formula guide shows the consistent method.
- Setting it and forgetting it. Life changes the target. Revisit annually.
- Treating it as a pass/fail line. Being at 60% of your FIRE number with two decades left isn’t failure — it’s a plan in progress.
How to Track Your Progress
Knowing your FIRE number is step one; watching yourself approach it is what keeps the plan alive:
- Track invested assets, not net worth. Your FIRE progress counts only withdrawal-generating investments — 401(k)s, IRAs, HSAs, brokerage. Home equity and emergency funds stay out of the numerator.
- Watch the ratio, not the dollar gap. “I’m at 38% of my FIRE number” stays meaningful through raises and market swings in a way “I’m $750,000 short” doesn’t.
- Recalculate annually. Spending changes, family changes, and guaranteed income estimates all move the target. A FIRE number is a living figure, not a tattoo.
- Celebrate the intermediate milestones. Coast FIRE is the big one — it’s the moment continued saving becomes optional. Couples should track one combined number (method here: Coast FIRE for couples).
What to Do Once You Know Your Number
A FIRE number without a next action is trivia. In order:
- Verify it. Run your spending through the 25× formula, then sanity-check with conservative variants (28× for early retirement, per our Rule of 25 guide).
- Find your Coast FIRE number. This is today’s actionable target — the invested balance after which compound growth finishes the job alone. A 30-year-old needs about $319,000 to coast to $1M by 60; see your age on our Coast FIRE by age pages.
- Close the gap. If you’re short, the levers are contributions, time, spending, and returns (in roughly that order of reliability).
- Recheck yearly and after every major life change.
Why the Number Matters More Than the Movement
You don’t have to identify with FIRE as a lifestyle to benefit from knowing your number. It converts an anxiety (“will I ever be able to stop working?”) into a measurable target with a date attached. It makes trade-offs concrete: a $200/month subscription habit is $60,000 of extra FIRE number; a paid-off mortgage might remove $500,000. And it unlocks the intermediate milestones — especially Coast FIRE — that deliver most of the psychological freedom decades before the full number arrives. Even if you never plan to retire early, knowing the point at which work becomes optional changes how every career decision feels.
The Bottom Line
Your FIRE number turns “someday” into arithmetic: spending × 25, minus what guaranteed income covers, adjusted for how long your retirement needs to last. Whether your flavor is Lean, Coast, Barista, or Fat, the multiplication is the same — only the inputs differ.
Get your number in the next 30 seconds: enter your age, spending, and current investments into the Coast FIRE calculator. It shows your FIRE number, your (smaller, nearer) Coast FIRE number, and the exact date your investments cross the coast line — the day saving for retirement becomes optional.