How to Calculate Your FIRE Number

By the FIRE Engine editorial team · Updated July 5, 2026 · 5 min read

To calculate your FIRE number, divide your expected annual expenses by your safe withdrawal rate. At the classic 4% rate, that's simply 25 times your annual spending. This one number is the finish line of financial independence: once your invested assets reach it, your portfolio can cover your lifestyle indefinitely. Here's how to work it out.

Key takeaways

FIRE number = annual expenses ÷ safe withdrawal rate.
At 4%, that equals 25× your annual expenses.
Every $1,000 you cut from yearly spending drops the target by ~$25,000.
A lower withdrawal rate (3.5%, 3.25%) means a bigger, safer number.

Step 1: Estimate your annual expenses

Start with what you'll actually spend in a typical retirement year, in today's dollars. Add up housing, food, transportation, insurance, healthcare, and discretionary spending. Adjust for known changes — maybe the mortgage is gone, but travel or health costs rise. This number matters more than your income: FIRE is built on spending, not earning.

Step 2: Pick your withdrawal rate

The safe withdrawal rate is the share of your portfolio you'll draw each year. The benchmark is 4%. If you're retiring early and want more cushion for a 40–50 year horizon, use 3.5% or 3.25%.

Step 3: Do the math

FIRE number = annual expenses ÷ withdrawal rate

Worked examples at different spending levels and a 4% rate:

$40,000 expenses ÷ 0.04 = $1,000,000
$50,000 expenses ÷ 0.04 = $1,250,000
$80,000 expenses ÷ 0.04 = $2,000,000

Switch to a 3.5% rate and $50,000 of expenses needs about $1,430,000 instead — the safety margin has a price.

Skip the math: the free FIRE Calculator computes your FIRE number from your expenses and withdrawal rate, then projects the exact age you'll reach it based on your savings. Adjust any input and watch the target move in real time.

Why expenses are the biggest lever

Because the multiplier is 25×, cutting expenses is unusually powerful. Trim $4,000 from your annual spending and your FIRE number falls by roughly $100,000 — and you also free up cash to invest, so you reach the lower target faster. That double effect is why frugality accelerates FIRE more than a raise of the same size.

What to include in your expenses (and what people forget)

The accuracy of your FIRE number depends entirely on getting your expense estimate right, and this is where most people slip. A realistic figure should account for more than your day-to-day bills:

Taxes. Withdrawals from traditional retirement accounts are taxable income. If you'll owe tax in retirement, your FIRE number needs to cover your spending plus that tax, not just your lifestyle.
Healthcare. For early retirees in the US, this is often the single biggest wild card before Medicare eligibility. Build in a realistic premium and out-of-pocket estimate.
Lumpy, irregular costs. New roofs, car replacements, and major home repairs don't show up in a normal month but are guaranteed over decades. Average them into an annual figure.
A buffer. Adding a 5–10% cushion to your expense estimate quietly protects you from underestimating — and from lifestyle drift once you have free time to fill.

A useful shortcut: track your actual spending for 6–12 months, then adjust for the changes retirement will bring. Real data beats guesses every time.

Adjust the number for your type of FIRE

The 25× formula is the baseline, but the target shifts depending on the version of early retirement you're aiming for:

Lean FIRE — a minimalist budget produces a smaller number you reach sooner.
Fat FIRE — a generous, no-compromise lifestyle needs a much larger portfolio.
Coast FIRE — you calculate the full number, then discount it back to what you need invested today for growth alone to get you there.
Barista FIRE — subtract expected part-time income from expenses first; your portfolio only funds the gap.

Same core math, four different finish lines. Each has its own calculator so you can see the exact figure for your plan.

Common mistakes when calculating your FIRE number

Using income instead of expenses. Your number is built on what you spend, not what you earn. Two people earning the same can have wildly different FIRE numbers.
Forgetting taxes. A $50,000 lifestyle may need $60,000+ of withdrawals once taxes are counted.
Chasing false precision. Your number is an estimate that will move as life changes. Recalculate every year or two rather than agonizing over a perfect figure.
Ignoring the withdrawal-rate trade-off. A lower rate is safer but demands a bigger portfolio — see sequence-of-returns risk for why that safety can be worth it.

Frequently asked questions

How do you calculate your FIRE number?

Divide your expected annual expenses by your safe withdrawal rate. At a 4% withdrawal rate this equals 25 times your annual spending. For example, $50,000 ÷ 0.04 = a $1,250,000 FIRE number.

Should I use current or future expenses?

Use the annual expenses you expect in retirement, in today's dollars. Adjust for changes you anticipate — a paid-off mortgage, healthcare, travel — then let inflation be handled by the withdrawal rule.

What withdrawal rate should I use?

4% is the traditional benchmark and gives a 25× target. Early retirees with a 40-plus year horizon often use 3.5% (about 29×) or 3.25% (about 31×) for a larger safety margin.

About the author: This article was written and reviewed by the FIRE Engine editorial team — independent writers who follow the FIRE movement and run these numbers on their own finances. We show the formula behind every calculation and cite primary sources. Learn more about our editorial standards.

Disclaimer: This article is for educational purposes only and is not financial advice. Consult a qualified professional before making financial decisions.