Every FIRE plan starts with spending, not income. The Cost FIRE Calculator takes your annual expenses and a safe withdrawal rate and turns them into the one number that matters: the portfolio size that funds your life forever. It then shows how many years of your income that number takes, and lays lean, standard, and fat FIRE targets side by side.

Three inputs, eight answer rows. You enter annual spending, pick a withdrawal rate between 3 and 5 percent, and enter your annual income. The calculator does the division, frames the timeline, and shows how a leaner or richer lifestyle changes both the target and the years.

What Does the Cost FIRE Calculator Do?

The calculator answers the foundational FIRE question: how much must I have invested to live off my portfolio? It divides your annual spending by your chosen safe withdrawal rate to produce your standard FIRE number — the portfolio that funds your expenses indefinitely.

Then it scales that answer into three tiers. Lean FIRE uses 75 percent of your spending for a simpler life; fat FIRE uses 150 percent for a comfortable one. Each tier gets its own number and its own years-to-FIRE figure, measured in years of your current income.

How to Use the Cost FIRE Calculator

Enter your true annual spending — what your life costs for a full year, not what you wish it cost.

Pick a safe withdrawal rate from the dropdown: 3 percent is conservative, 4 percent is the standard, 5 percent is bold. Then enter your annual income, press Calculate, and read the rows. The years figures assume every dollar of income is saved, so treat them as the theoretical minimum timeline.

The FIRE Number Formula

The entire calculator rests on one division. The formula is:

FIRE number = annual spending / safe withdrawal rate

Spend $60,000 a year with a 4 percent withdrawal rate and the number is $60,000 / 0.04, which is $1,500,000. The logic is simple: a $1,500,000 portfolio yielding 4 percent produces $60,000 a year, covering your spending while the principal survives.

The Years-to-FIRE Formula

The timeline figure is another division: your FIRE number divided by your annual income. The formula is:

Years to FIRE = FIRE number / annual income

A $1,500,000 number on a $120,000 income takes $1,500,000 / $120,000, or 12.5 years. This is the absolute fastest timeline — it assumes a 100 percent savings rate, zero taxes, and zero investment growth. Read it as a lower bound, not a schedule.

Worked Example: $60,000 Spending, 4% Rate, $120,000 Income

A professional spends $60,000 a year, picks the standard 4 percent rate, and earns $120,000 a year. The standard number: $60,000 / 0.04 equals $1,500,000. The tiers: lean FIRE is $45,000 / 0.04, or $1,125,000; fat FIRE is $90,000 / 0.04, or $2,250,000.

The timelines: $1,125,000 / $120,000 is 9.4 years to lean FIRE; $1,500,000 / $120,000 is 12.5 years to standard; $2,250,000 / $120,000 is 18.8 years to fat. Trimming spending by a quarter buys the goal 3.1 years sooner; the fat lifestyle costs 6.3 extra years.

Worked Example: $40,000 Spending, 3.5% Rate, $100,000 Income

A cautious saver spends $40,000 a year, chooses a conservative 3.5 percent rate, and earns $100,000 a year. The standard number: $40,000 / 0.035 equals $1,142,857. The tiers: lean FIRE is $30,000 / 0.035, or $857,143; fat FIRE is $60,000 / 0.035, or $1,714,286.

The timelines: $857,143 / $100,000 is 8.6 years to lean FIRE; $1,142,857 / $100,000 is 11.4 years to standard; $1,714,286 / $100,000 is 17.1 years to fat. The conservative rate pushes every number up — yet the timelines stay short because her income dwarfs her spending.

Worked Example: $80,000 Spending, 5% Rate, $160,000 Income

A high earner spends $80,000 a year, accepts an aggressive 5 percent rate, and earns $160,000 a year. The standard number: $80,000 / 0.05 equals $1,600,000. The tiers: lean FIRE is $60,000 / 0.05, or $1,200,000; fat FIRE is $120,000 / 0.05, or $2,400,000.

The timelines: $1,200,000 / $160,000 is 7.5 years to lean FIRE; $1,600,000 / $160,000 is 10 years to standard; $2,400,000 / $160,000 is 15 years to fat. The bold 5 percent rate compresses every target — but a higher withdrawal rate is a bet that history's good outcomes repeat.

Worked Example: $50,000 Spending, 4.5% Rate, $90,000 Income

A mid-career worker spends $50,000 a year, picks a middle-ground 4.5 percent rate, and earns $90,000 a year. The standard number: $50,000 / 0.045 equals $1,111,111. The tiers: lean FIRE is $37,500 / 0.045, or $833,333; fat FIRE is $75,000 / 0.045, or $1,666,667.

The timelines: $833,333 / $90,000 is 9.3 years to lean FIRE; $1,111,111 / $90,000 is 12.3 years to standard; $1,666,667 / $90,000 is 18.5 years to fat. The middle path splits the difference between the cautious 3.5 percent example and the bold 5 percent one.

Lean vs. Standard vs. Fat FIRE

The three tiers are not three different philosophies — they are the same math at three spending levels. Lean FIRE assumes you can live happily on 75 percent of current spending: smaller home, fewer luxuries, more time than money. Fat FIRE assumes 150 percent: travel, generosity, a buffer against the unknown.

The calculator's rows make the trade visible. In the $60,000 example, lean FIRE arrives in 9.4 years and fat FIRE in 18.8 — the comfortable life costs double the time.

Choosing Your Safe Withdrawal Rate

The withdrawal rate is the calculator's risk dial. Three percent is the fortress: it survived nearly every historical scenario, including long retirements and bad starting years. Four percent is the convention: the Trinity Study's headline figure. Five percent is the gamble: workable in good sequences, dangerous in bad ones.

The cost of caution is concrete. At $60,000 of spending, 3 percent demands $2,000,000 while 5 percent asks only $1,200,000 — an $800,000 difference for two points of perceived safety.

The Savings-Rate Caveat in the Years Figure

The years-to-FIRE rows carry the calculator's biggest assumption: every dollar of income saved and invested. Nobody does this — taxes, rent, and food take their share first. The figure is a theoretical floor, and your real timeline stretches with every dollar you actually spend.

Here is the honest translation: the years figure divided by your real savings rate gives a rough realistic timeline. 12.5 years at a 50 percent savings rate becomes about 25 years, before investment growth shortens it again. Use the rows comparatively, not literally — they rank the tiers perfectly even though no single figure is your actual calendar date.

Common Cost FIRE Calculator Mistakes

The number-one mistake is entering income instead of spending in the spending field. The FIRE number is built from expenses; income only sets the timeline. Swapping them produces a "number" that funds your salary, not your life.

The second mistake is using today's spending without adjusting for retirement. Mortgages end, commuting costs vanish, kids leave — but healthcare rises. Build the retirement budget first, then enter that figure, not last year's bank total.

Where Cost FIRE Numbers Are Useful

The FIRE number converts an abstract dream into a concrete target. "I want to retire early" is a wish; "$1,500,000 at 4 percent" is a plan with a finish line.

It is also a decision filter. Every major expense can be translated into FIRE time: a $30,000 car on a $120,000 income is a quarter of a year of freedom. Some purchases survive that translation; many do not, and the number makes the trade impossible to ignore.

How to Interpret Your Result

Start with the standard FIRE number — your headline target, built from your actual spending at a defensible withdrawal rate. Then read the tiers as a menu: lean shows what freedom costs at minimum, fat shows what comfort costs at maximum, and the gap between them is the price of lifestyle.

Finally, discount the years figures for reality. Divide them by your actual savings rate for a rough honest timeline, then let investment growth pull it back down. The calculator gives you the skeleton of the plan; your savings rate and your returns put flesh on it.

What to Do With Your FIRE Number

First, write it down somewhere you will see it. A target that lives only in a calculator tab has no power; a number on the fridge changes daily decisions about spending and saving.

Second, convert it into a savings-rate goal: your FIRE number divided by the years you will give yourself, adjusted for growth, becomes an annual savings target — and that target becomes a monthly automatic transfer.

Frequently Asked Questions

1. What is a FIRE number?

Your FIRE number is the invested portfolio size that funds your annual spending forever at your chosen withdrawal rate. At $60,000 of spending and 4 percent, it is $1,500,000 — a portfolio that generates $60,000 a year while the principal endures.

2. Why does the calculator use 75% and 150% for lean and fat FIRE?

They are the community's standard definitions: lean FIRE is a simplified life at roughly three-quarters of normal spending, fat FIRE is a comfortable life at roughly one-and-a-half times.

3. Is the 4% rule still safe?

It remains the standard starting point, grounded in the Trinity Study's historical testing. Critics note it was built on 30-year retirements and US market history, so early retirees often prefer 3.5 percent. Run your spending at both rates and compare the price of caution.

4. Do the years figures include investment growth?

No. The years-to-FIRE rows are simple division — FIRE number divided by income — assuming a 100 percent savings rate and zero growth. Growth shortens real timelines substantially, while taxes and actual spending lengthen them. Treat the rows as a comparative ruler between tiers, not a calendar.

5. Should I use gross or net income?

Use the figure that matches how you think about saving. Gross income makes the years figure optimistic, since taxes take a cut you cannot save. Net take-home income gives a more honest timeline. Either way, the 100-percent-savings assumption means the figure is a floor, not a forecast.

6. Does the FIRE number include taxes in retirement?

Only if your spending input includes them. Withdrawals from pre-tax accounts are taxed, so $60,000 of lifestyle spending may need $70,000 of withdrawals. Either inflate the spending input to cover retirement taxes or plan the account mix accordingly.

7. What about inflation?

The FIRE number is in today's dollars, and the 4% rule was designed in inflation-adjusted terms: you withdraw 4 percent the first year, then adjust that amount for inflation afterward. As long as your spending input reflects today's costs, the number is already inflation-aware by construction.

8. Can I reach FIRE with a low income?

Yes — spending matters more than income. The $40,000 spender earning $100,000 reaches standard FIRE in 11.4 theoretical years, nearly matching the $80,000 spender earning $160,000 at 10 years. Control spending first; income is the second lever.

9. What is the difference between lean FIRE and Coast FIRE?

Lean FIRE is a smaller full-retirement number — you quit work entirely on a lean budget. Coast FIRE is a different strategy: your current savings grow into the full number later, so you keep working but stop saving. Lean FIRE ends work sooner on less; Coast FIRE keeps work but removes the savings burden.

10. Should couples combine their numbers?

Usually yes: combine household spending and household income, then run the calculator once. Shared expenses like housing make the household number smaller than two individual numbers added together. If finances are separate, run it individually — but agree on the withdrawal rate first.

11. Why is my fat FIRE timeline so much longer?

Because fat FIRE demands 50 percent more spending, which means 50 percent more portfolio — and the years figure scales linearly with the number. In the $60,000 example, fat FIRE at $2,250,000 takes 18.8 years versus 12.5 for standard. Every lifestyle upgrade is priced in years.

12. Can I change my withdrawal rate after retiring?

Yes, and flexible retirees often do — spending less in down markets and more in good ones stretches any portfolio further than a rigid rate. Treat 4 percent as the starting guardrail and adjust with reality.

13. Does the calculator account for Social Security?

Not directly, but you can fold it in: subtract your expected annual benefit from your annual spending before entering it. Spend $60,000, expect $20,000 from Social Security, enter $40,000 — the FIRE number drops from $1,500,000 to $1,000,000 at 4 percent.

14. What if my spending changes a lot year to year?

Use a realistic long-run average, weighted toward retirement years rather than today's peak-spending years. If spending swings wildly, run the calculator at both the low and high ends — the two results bracket your true target.

15. Is FIRE only for high earners?

No. The math rewards the gap between income and spending, not income alone. A $60,000 earner spending $30,000 saves half their income — the same savings rate as a $200,000 earner spending $100,000, and a similar timeline. High earners get there with less discipline; everyone else gets there with more intention.