What is a FIRE number?
Your FIRE number is the size of invested portfolio at which work becomes optional. Not “retire rich,” not “replace every dollar of your salary” — just the point where a diversified pile of index funds can fund your actual life, at your actual spending, indefinitely. It's the single most useful number in personal finance because it converts a vague dream (“someday I'll have enough”) into a target you can measure progress against every month.
The concept comes from the Financial Independence, Retire Early movement, but you don't need to want early retirement to benefit from knowing it. Even if you love your job, your FIRE number is the price of not needing one — leverage in negotiations, insurance against layoffs, and permission to take risks you'd otherwise refuse.
The formula, explained honestly
At its core the calculation is one division:
FIRE number = annual spending ÷ safe withdrawal rate
- Annual spending. What you actually spend, not what you earn. This calculator takes monthly spending and grosses it up for retirement taxes if you set a tax rate — because a $42,000 lifestyle funded from a traditional 401(k) needs more than $42,000 of pre-tax withdrawals.
- Safe withdrawal rate (SWR). The percentage of your portfolio you can withdraw each year, adjusted for inflation, with very high odds of the money lasting 30+ years. The classic figure is 4%, from the Trinity Study's historical simulations; conservative early retirees use 3.25–3.5%.
Spend $3,500 a month ($42,000 a year) at a 4% withdrawal rate? $42,000 ÷ 0.04 = $1,050,000. That's the whole engine — everything else on this page exists because the two inputs hide subtleties. Inflation means the number must be stated in today's dollars and grown alongside prices; market returns are uncertain, which is why the projection below uses real (inflation-adjusted) returns converted properly as (1 + nominal) ÷ (1 + inflation) − 1, not the naive subtraction that overstates a typical 30-year portfolio by about 3–4% at these assumptions.
A worked example
Devon spends $3,500 a month, has $60,000 invested, saves $2,000 a month, and assumes 7% nominal returns with 3% inflation — a real return near 3.9% after correct conversion.
- FIRE number: $42,000 ÷ 4% = $1,050,000 in today's dollars.
- At $2,000/month and ~3.9% real growth, the projection crosses $1.05M around age 56 — about 24 years of saving from 32.
- Every $100/month of extra savings pulls the finish roughly a year closer. Every $100/month cut from spending does double duty: faster savings and a FIRE number lower by $30,000.
That last asymmetry is why frugality dominates income-chasing in FIRE math: spending has two levers, income has one.
Reading your verdict
The panel compares today's investments against where compounding says you should be, then gives one of three answers. Reached: you're past your number — withdrawals at your SWR cover your spending, and further work is a choice. On track: not there yet, but your current contributions arrive on time; the subline names the crossing age. Behind: this pace falls short, so the panel prices the fix — an extra monthly contribution or a later date, whichever feels cheaper. Flip the crash test to replay everything with your portfolio down 30% and see if the plan survives a bad decade arriving early.
Common mistakes this calculator avoids
Counting home equity you intend to keep living in (it can't be withdrawn). Using salary instead of spending (your number doesn't care what you earn). Assuming nominal returns while ignoring inflation. Forgetting taxes on traditional retirement accounts. And the sneakiest one: recalculating after every raise and inflating the target along with lifestyle — the number only stays meaningful if the spending input stays honest.
Frequently asked questions
What exactly is a FIRE number?
It's the invested portfolio size that lets you live off withdrawals forever without ever running out. The standard estimate is your annual spending divided by your safe withdrawal rate — spend $42,000 a year at a 4% withdrawal rate and your FIRE number is $1,050,000.
Is the 4% rule the right withdrawal rate for me?
The 4% figure comes from historical simulations of US stock-and-bond portfolios retiring into every market since 1926. It's a reasonable starting point, not a law. Early retirees often plan on 3–3.5% for extra safety; those with pensions or Social Security covering part of their spending can justify higher effective rates. The calculator's advanced settings let you test both directions.
Why is my FIRE number different on other calculators?
Most calculators skip two adjustments this one makes. First, real returns: we convert nominal return minus inflation using (1 + nominal) ÷ (1 + inflation) − 1, which avoids the ~6% overstatement the naive subtraction introduces over 30 years. Second, taxes: set a retirement tax rate and we gross up your spending so the target covers pre-tax withdrawals, not just take-home spending.
Should my FIRE number include my house or emergency fund?
No. The number counts only liquid, income-producing investments you'll actually draw from — index funds, ETFs, dividend stocks, bonds. Home equity you plan to keep living in, cash buffers, and cars don't generate retirement withdrawals, so including them flatters the progress bar while hiding the real gap.
What if I can't save enough to reach my number?
The verdict panel shows your two levers when you're behind: the extra monthly contribution that lands you at your target age, or how many years later your current pace gets you there — whichever feels cheaper. There's also a third lever the math can't compute: spending less changes the target itself. Dropping monthly spending by $500 cuts a typical FIRE number by $150,000.
Keep going
Know your number but want a checkpoint sooner? Try the Coast FIRE calculator or the savings rate calculator, or head back to the FireVerdict hub.