July 31, 2026 · Updated September 5, 2026 · 9 minute read
By Nethaven Team · Personal finance research & product team
What Is Your FIRE Number? How to Calculate It
Estimate your FIRE number from annual spending and a withdrawal rate. Understand the 25x shortcut, retirement horizon, taxes, and investment risks.
Your FIRE number is an estimate of the invested assets needed to fund retirement spending. At a 4% starting withdrawal rate, $48,000 a year implies $1.2 million, or 25 times spending. The shortcut draws on 30-year U.S. stock-and-bond retirement research. Longer horizons, allocation, taxes, and market risk can change the target; it is not a guarantee. Withdrawal research models a finite horizon and a probability of success.
The arithmetic behind a FIRE number takes about ten seconds. Choosing the inputs takes longer. Review a full year of expenses so insurance renewals, repairs, and holidays are included. An illustrative 20% error in annual spending produces the same 20% error in the target when the withdrawal rate is held constant.
What is a FIRE number?
A FIRE number is a planning target for the portfolio that would cover your spending under stated withdrawal and investment assumptions. FIRE stands for financial independence, retire early. Reaching the target is a reason to review whether the plan can support reduced paid work, including how you would respond to poor returns or higher costs.
Use assets available to fund the plan. Access restrictions on retirement accounts need a bridge strategy for early retirement. If rental income reduces the spending your portfolio must cover, do not also apply a portfolio withdrawal rate to the same property value. A primary residence belongs in total net worth, but only planned sale, downsizing, or rental proceeds belong in this spending calculation.
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. Compare several assumptions, such as 4%, 3.5%, and 3%, and test them against your horizon and allocation. A lower rate increases the target but does not guarantee success.
- 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. The effect on the retirement date still depends on your starting assets, contributions, and actual returns.
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 | Illustrative target at 4% |
|---|---|---|
| Lean FIRE | Lower spending, illustrated here at $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 | Depends on net work income |
Coast FIRE is the one worth understanding early, because it estimates how much existing assets might grow without further contributions. The result depends on time and returns. 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?
Check these assumptions before relying on the target.
- Guessed spending. Include irregular costs that a typical-month estimate can miss.
- Counting the primary residence. It inflates the asset side without producing any withdrawable income.
- Using pre-tax portfolio balances. In the U.S., taxable withdrawals from traditional retirement accounts must also cover the tax bill. Include expected taxes in the spending target; treatment depends on account type and jurisdiction.
- Ignoring health coverage. For anyone retiring before Medicare eligibility in the US, price the coverage you expect to use and include it in the spending plan.
- Assuming spending stays flat forever. Test higher medical, care, and housing costs as well as lower discretionary spending.
What do you do with the number once you have it?
Translate the target into a contribution plan. Estimate how long current assets and regular contributions might take to reach it, then compare several return and inflation assumptions. Both savings and investment returns affect that projection.
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 in Nethaven
Keep accounts, budgets, debt, goals, and subscriptions connected between reviews on iOS, Android, and web.
Frequently asked questions
What is a FIRE number?
A FIRE number is an estimate of invested assets needed to fund retirement spending under a chosen withdrawal strategy. Annual spending times 25 corresponds to a 4% first-year withdrawal, with later withdrawals adjusted for inflation in the traditional rule. The 30-year U.S. research horizon, allocation, taxes, and market risks matter; the target does not promise indefinite funding.
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?
A primary residence counts toward total net worth but does not directly fund portfolio withdrawals. Include proceeds only if your plan involves selling, downsizing, or renting it. If net rental income reduces your spending gap, do not also count the same property as part of the portfolio supporting withdrawals.
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. The traditional 4% rule examined historical 30-year U.S. retirement periods with stock-and-bond portfolios. A 40- or 50-year retirement needs separate analysis. Testing a lower withdrawal rate raises the target, but future returns and personal costs can still differ from the assumptions.
What is the difference between a FIRE number and a Coast FIRE number?
A FIRE number estimates the portfolio needed to support withdrawals under your plan. A Coast FIRE number estimates what existing assets might grow into by a later date without further contributions. Neither milestone guarantees that you can stop saving or working; review returns, inflation, taxes, access restrictions, and spending before changing the plan.