July 31, 2026 · 9 minute read
By Nethaven Team · Personal finance research & product team
What Is Your FIRE Number? How to Calculate It
Your FIRE number is annual spending times 25. How to calculate it from measured expenses, why lean, fat and coast FIRE differ, and when to recalculate.
Your FIRE number is the portfolio size that can fund your spending indefinitely: annual expenses multiplied by 25, based on a 4% withdrawal rate. A household spending $48,000 a year needs roughly $1.2 million. The multiplier changes with your withdrawal rate, and the spending figure should be measured, not estimated.
The arithmetic behind a FIRE number takes about ten seconds. The reason most people's numbers are wrong has nothing to do with the arithmetic and everything to do with the input. Ask someone what they spend in a year and the answer is almost always a rounded guess built from remembered fixed costs, which leaves out the irregular spending that makes up a surprisingly large share of a real budget. A 20% error in the spending figure is a 20% error in the target, and at these amounts that is measured in hundreds of thousands of dollars.
What is a FIRE number?
A FIRE number is the amount of invested assets at which your portfolio can cover your living costs without you adding to it. Past that point, work becomes a choice rather than a requirement. It comes from the FIRE movement, short for financial independence, retire early, though plenty of people calculate one with no intention of retiring early at all. Knowing the number changes how you read every other financial decision.
The important boundary is that a FIRE number applies to assets you can actually draw from. Brokerage accounts, retirement accounts, and income property count. A primary residence does not, because you cannot spend 4% of your kitchen. That distinction is why a FIRE number and net worth are related but not interchangeable, and why tracking them separately matters.
How do you calculate your FIRE number?
Four steps, and the first one is the only difficult one.
- Measure your actual annual spending. Not your budget, not your income minus savings, but what left your accounts over the last twelve months. Twelve months matters because it captures insurance renewals, holidays, car maintenance, and the annual subscriptions that never appear in a typical month.
- Adjust it for the life you are aiming at. Remove commuting costs and work clothes if those go away. Add health insurance if an employer currently covers it. Add or remove a mortgage payment depending on whether it will still be running.
- Pick a withdrawal rate. 4% is the default. 3.5% or 3% is common for anyone planning a retirement longer than thirty years.
- Divide 100 by that rate to get your multiplier, then multiply your adjusted spending by it. 4% gives 25x, 3.5% gives about 28.6x, and 3% gives about 33.3x.
A household with $48,000 of adjusted annual spending lands on $1.2 million at 4%, $1.37 million at 3.5%, and $1.6 million at 3%. Same life, same spending, a $400,000 spread driven entirely by how much margin you want. The FIRE number calculator runs these side by side along with a year-by-year projection.
Why does the spending figure matter more than the multiplier?
Because it works in both directions at once. Cutting $200 a month of recurring spending removes $2,400 from annual expenses, which drops the FIRE number by $60,000 at 25x. The same $200 also becomes $200 of additional monthly contributions. One change lowers the finish line and speeds you toward it simultaneously, which is why permanent reductions in fixed costs move a FIRE timeline far more than a good year in the market does.
This is also the argument for measuring rather than estimating. Subscriptions are the clearest example: they are individually small, collectively significant, and almost never included in a guessed annual spending figure. Nethaven's subscription tracking exists partly for this reason, since a recurring charge you forgot about is both an ongoing cost and a permanent addition to your target.
Do lean, fat, coast, and barista FIRE have different numbers?
Lean, regular, and fat FIRE use the same formula with different spending assumptions, so they produce different targets. Coast and barista FIRE are structurally different: they are not full targets at all, but intermediate milestones.
| Variant | What it assumes | Target on $48k spending |
|---|---|---|
| Lean FIRE | Deliberately low spending, often under $30k | ~$750k at $30k |
| Regular FIRE | Current adjusted spending maintained | $1.2M |
| Fat FIRE | Comfortable or expanded spending | ~$2.5M at $100k |
| Coast FIRE | Enough invested to grow into the full number unaided | Varies by years remaining |
| Barista FIRE | Portfolio covers part of spending, part-time work covers the rest | Partial, often 50-70% |
Coast FIRE is the one worth understanding early, because it usually arrives a decade or more before the full number and it changes what your savings rate needs to be right now. Coast FIRE explained covers the formula and the risks of stopping contributions too soon.
How often should you recalculate it?
Annually, plus after any event that permanently changes spending. The annual review is worth doing properly: pull the last twelve months of real expenses again rather than adjusting last year's figure by a guess at inflation, because the categories that drifted are usually not the ones you would have predicted.
Between those reviews, what changes is progress toward the number, not the number itself. Tracking that progress against a fixed target is the useful habit; recalculating the target every time the market moves is not. Keeping invested assets visible in one place, through portfolio tracking or a monthly balance review, is what makes the annual recalculation take twenty minutes instead of an afternoon.
What makes a FIRE number wrong?
Five errors account for most bad targets, and four of them make the number look better than it is.
- Guessed spending. The single largest source of error. Guesses skew low because irregular costs are forgettable by definition.
- Counting the primary residence. It inflates the asset side without producing any withdrawable income.
- Using pre-tax portfolio balances. Withdrawals from traditional retirement accounts are taxable, so a $1.2 million balance does not fund $48,000 of after-tax spending.
- Ignoring health coverage. For anyone retiring before Medicare eligibility in the US, this is frequently the largest single new expense and it is routinely left out.
- Assuming spending stays flat forever. It usually drops in later retirement and spikes around health events, which is an argument for margin rather than precision.
What do you do with the number once you have it?
Convert it into a rate rather than a destination. A target of $1.2 million is not actionable; a savings rate that reaches $1.2 million in eighteen years is. Savings rate is the dominant variable in every FIRE projection, far more than investment return assumptions, because it determines both how fast the portfolio grows and how small the target needs to be.
From there the mechanics are ordinary: automate contributions, keep fixed costs from creeping upward, and review annually. If you are starting from scratch, the first steps toward FIRE covers the sequence, and the 4% rule covers where the 25x multiplier came from and what it assumes.
Educational content, not personal financial advice. Withdrawal-rate research is based on historical US market data and specific portfolio assumptions; future returns, tax treatment, and personal circumstances vary. Consider professional advice before making retirement decisions.
Track this automatically in Nethaven so accounts, budgets, debt, goals, and subscriptions stay connected between reviews.
Frequently asked questions
What is a FIRE number?
A FIRE number is the portfolio value at which investment returns can cover your living costs indefinitely, so paid work becomes optional. The standard calculation is annual spending multiplied by 25, which corresponds to withdrawing 4% of the portfolio each year. It is a target for accumulated invested assets, not for total net worth.
How do taxes change my FIRE number?
They raise it, often substantially, and the standard formula ignores them. A $1.25 million balance held mostly in traditional retirement accounts does not fund $50,000 of after-tax spending, because withdrawals are taxed as income. The practical adjustment is to calculate the target from gross spending including expected tax, or to hold a mix of taxable, tax-deferred, and Roth accounts so withdrawals can be drawn from the most efficient source each year.
Should my FIRE number be based on income or spending?
Spending, always. Income tells you what arrives; spending tells you what the portfolio has to replace. Two households earning the same amount can have FIRE numbers that differ by hundreds of thousands of dollars because one spends far less than the other. Using income as the basis systematically overstates the target for anyone who saves aggressively.
Does my house count toward my FIRE number?
Usually not directly. A primary residence does not generate withdrawable income, so it does not help fund annual spending even though it adds to net worth. What it does change is the spending side: an owned home with no mortgage lowers annual expenses, which lowers the FIRE number itself. Rental property is different, since it produces income you can count.
Do lean FIRE and fat FIRE have different numbers?
Yes, because each describes a different annual spending level fed into the same formula. Lean FIRE typically assumes spending well below the national median, fat FIRE assumes a comfortable or high-spending retirement, and regular FIRE sits between them. The 25x multiplier does not change; the spending figure does, and it moves the target proportionally.
How often should I recalculate my FIRE number?
Once a year is enough for most people, plus after any event that permanently changes spending: a move, a child, paying off a mortgage, a change in health coverage. Recalculating monthly turns a long-term target into a source of anxiety, and the inputs rarely move enough in thirty days to justify it.
Is 25 times spending actually safe?
It is a starting estimate, not a guarantee. The 25x multiplier comes from research on 30-year US retirement periods, so it is less tested for retirements of 40 or 50 years and it assumes a stock-heavy portfolio. Many people planning early retirement use 28x to 33x, corresponding to 3% to 3.5% withdrawals, to build in margin.
What is the difference between a FIRE number and a Coast FIRE number?
The FIRE number is the full target that supports withdrawals today. The Coast FIRE number is the smaller amount that, left invested and untouched, would grow into the full FIRE number by your target retirement age without further contributions. Reaching Coast FIRE means you can stop saving; reaching FIRE means you can stop working.