TL;DR
Your FIRE number equals your annual spending multiplied by 25, based on the 4% safe withdrawal rate; someone spending $60,000 a year needs roughly $1,500,000 invested to retire, though active traders should adjust the multiple based on how much of their spending comes from trading income versus a portfolio.
Key Takeaways
- 1.The core formula is annual expenses x 25, derived from a 4% safe withdrawal rate.
- 2.Lean FIRE, Fat FIRE, Coast FIRE, and Barista FIRE all use the same formula with different expense assumptions.
- 3.A growing body of 2026 research suggests 3.5% is a safer withdrawal rate for retirements longer than 40 years, which raises your number to expenses x 28.5.
- 4.Active traders should calculate two numbers: a FIRE number assuming no trading income, and a lower Coast FIRE number if trading income continues part-time.
- 5.Volatility in a trading-heavy portfolio means your real FIRE number should include a cash buffer of 12 to 24 months of expenses beyond the base multiple.
Your FIRE number is how much you need invested before you can live off withdrawals instead of a paycheck. To find it, multiply your annual expenses by 25 for a standard 4% withdrawal rate, or by roughly 28.5 for the more conservative 3.5% rate several 2026 retirement studies now recommend.
I've run this calculation for my own trading income against a straight salary comparison, and the gap matters more than most FIRE calculators show. A calculator that only asks for your current savings and expected return misses how lumpy trading income actually is, and lumpy income needs a bigger buffer than a steady paycheck does.
What is a FIRE number and how do you calculate it?
A FIRE number is the portfolio size that lets you cover your annual expenses indefinitely by withdrawing a fixed percentage each year, without running out of money over a multi-decade retirement. The standard calculation is annual expenses divided by your target withdrawal rate, most commonly 4 percent.
If you spend $50,000 a year, dividing by 0.04 gives you $1,250,000. That's the same as multiplying $50,000 by 25, which is why most FIRE calculators use the shorthand 'expenses times 25' instead of the division form.
| Annual expenses | FIRE number at 4% rule | FIRE number at 3.5% rule |
|---|---|---|
| $40,000 | $1,000,000 | $1,142,857 |
| $60,000 | $1,500,000 | $1,714,286 |
| $80,000 | $2,000,000 | $2,285,714 |
| $100,000 | $2,500,000 | $2,857,143 |
A retiree spending $80,000 a year needs $2,000,000 under the traditional 4% rule, but $2,285,714 under the more conservative 3.5% rate now favored by several 2026 retirement-planning studies for horizons past 40 years.
One detail most quick calculators skip: the 4% figure is your first-year withdrawal, and every year after that you adjust the dollar amount for inflation, not the percentage. If inflation runs 3% in your second year, you withdraw 3% more dollars than the prior year, keeping your purchasing power flat even as the raw withdrawal rate on your then-current balance drifts up or down with market performance.
How does the 4% rule actually determine your number?
The 4% rule comes from the Trinity Study, which tested historical stock and bond returns to find a withdrawal rate that survived 30-year retirement periods without depleting the portfolio in the vast majority of scenarios. A 4% initial withdrawal, adjusted for inflation each year after, held up in roughly 95 percent of rolling 30-year historical periods.
The rule was built for 30 years, not 50
If you're pursuing FIRE in your 30s or 40s, your retirement could run 50 years or longer. The original Trinity Study data covers 30-year windows, which is part of why some planners now recommend a lower withdrawal rate for early retirees.
The math behind the rule assumes a portfolio mostly in stocks and bonds, rebalanced annually, with withdrawals rising only with inflation. It does not assume you'll earn side income, which is exactly where traders and part-time earners can adjust the model in their favor.
A 4% withdrawal rate survived roughly 95 percent of historical 30-year periods in the original Trinity Study, which is the entire statistical foundation the FIRE movement's core formula rests on.
What are Lean FIRE, Fat FIRE, Coast FIRE, and Barista FIRE numbers?
FIRE isn't one number. The same 25x formula applies across several variants, and which one applies to you depends on your target lifestyle and whether you plan to keep earning any income after hitting your number.
| FIRE type | Typical annual expenses | Approx. FIRE number (4% rule) | Assumes continued income? |
|---|---|---|---|
| Lean FIRE | $25,000-$40,000 | $625,000-$1,000,000 | No |
| Regular FIRE | $40,000-$80,000 | $1,000,000-$2,000,000 | No |
| Fat FIRE | $100,000+ | $2,500,000+ | No |
| Coast FIRE | Varies | Enough invested today to grow untouched to a full number by a target age | Yes, covers current expenses |
| Barista FIRE | Varies | Partial FIRE number plus part-time income covering the gap | Yes, part-time |
Coast FIRE is the most relevant variant for traders who don't want to stop working entirely; it asks how much you need invested right now so that, left untouched, compound growth alone gets you to a full FIRE number by a target retirement age, even if you cover current living costs with active income.
How to calculate your FIRE number step by step
Calculating your FIRE number
- 1
Track 12 months of real expenses
Pull actual spending from bank and card statements rather than estimating; most people underestimate annual spending by 15 to 20 percent when they guess.
- 2
Separate essential from discretionary spending
This split matters for Lean FIRE versus regular FIRE planning and shows you where the number is flexible.
- 3
Pick your withdrawal rate
Use 4% for a 30-year retirement horizon or 3.5% if you're retiring before age 50 and expect a 40-plus year retirement.
- 4
Multiply annual expenses by 25 (or 28.5 for 3.5%)
This is your base FIRE number before adjusting for other income sources.
- 5
Subtract any guaranteed income
Rental income, a pension, or reliable part-time consulting reduces the portfolio withdrawal you need, lowering your number.
- 6
Add a volatility buffer if income is irregular
Traders and freelancers should add 12 to 24 months of expenses in cash or short-term bonds on top of the base number.
Someone who tracks real spending instead of estimating typically finds their true annual expenses run 15 to 20 percent higher than a rough guess, which means a rough FIRE number is usually too low before you've even picked a withdrawal rate.
How does active trading income change your FIRE number?
Most FIRE calculators assume a W-2 salary that stops entirely at retirement. Active traders rarely fit that model cleanly, since trading income can continue part-time after leaving a full-time job, but it's also more volatile month to month than a paycheck.
Pros
- Trading income that continues post-FIRE can lower your required portfolio size, similar to Barista FIRE
- A profitable trading account can be counted as a partial income stream when calculating a Coast FIRE number
- Portfolio-based FIRE calculations already assume market volatility, so a trading habit doesn't change the underlying math
Cons
- Trading income is far less predictable than a salary; a bad quarter can mean $0 in supplemental income right when you need it
- Relying on trading profits to lower your FIRE number assumes those profits persist for 20-plus years, which most trading track records don't demonstrate
- Sequence-of-returns risk compounds if you're also drawing down a trading account during a down year in the broader market
Sequence-of-returns risk makes this worse for traders specifically. If your trading account has a losing year that overlaps with a broader market downturn, you could end up drawing down both your portfolio and your trading capital in the same window, which is exactly the scenario a cash buffer is meant to prevent.
A safer approach for active traders is to calculate a full FIRE number assuming zero trading income, then treat any trading profit as upside rather than a line item that lowers the target, since a 20-year trading track record with guaranteed positive returns doesn't exist.
What safe withdrawal rate should you actually use in 2026?
The 4% rule remains the most-cited FIRE benchmark, but retirement researchers have refined it over the past decade. Updated studies published through 2026 generally recommend somewhere between 3.3% and 3.8% for retirements expected to last 40 years or more, versus the 30-year horizon the original 4% figure was tested against.
Use a range, not a single number
Calculate your FIRE number at both 4% and 3.5%. Treat the 4% number as your minimum target and the 3.5% number as your comfortable target, then keep working or trading between the two.
Retiring at 35 with a 55-year time horizon is a fundamentally different math problem than retiring at 65 with a 25-year horizon, which is the single biggest reason the FIRE community has moved away from treating 4% as a universal number.
Common mistakes when calculating your FIRE number
The formula itself is simple enough to do on a napkin. Most of the errors that blow up a FIRE plan happen in the inputs feeding that formula, not in the multiplication, which is why it's worth double-checking each of these before you treat your number as final.
- Using pre-tax income instead of actual after-tax spending to calculate the multiple
- Ignoring healthcare costs before Medicare eligibility, which can add $10,000 to $20,000 a year for early retirees
- Assuming trading or side income will reliably continue for decades without a track record to support it
- Skipping a cash buffer, leaving no cushion for a market downturn in the first five years of withdrawals
- Forgetting to adjust the number for a specific city's cost of living if retirement plans include relocating
Healthcare alone can add $10,000 to $20,000 a year to an early retiree's budget before Medicare eligibility at 65, which is often the single largest line item FIRE calculators leave out by default.
The verdict
Start with the simple version: annual expenses times 25. Then run it again at 28.5x if you're retiring before 50. Subtract any income you're confident will continue, add a cash buffer if that income includes trading profits, and you'll have a number that's realistic rather than optimistic. The formula takes five minutes; getting an honest expense number takes the other 95 percent of the work.
For most people pursuing FIRE with a mix of salary, savings, and trading income on the side, the safest number to plan around is the full 25x-to-28.5x multiple with zero trading income assumed, treating any trading profit as an accelerant rather than a load-bearing part of the plan.
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