FIRE Movement Math: How Much Do You Need to Retire Early?

The FIRE Formula

FIRE Number = Annual Spending × 25

This derives from the 4% rule: If you need $40,000/year and can safely withdraw 4% from your portfolio, you need a $1,000,000 portfolio ($1,000,000 × 4% = $40,000).

Conversely: FI Number / 25 = Safe annual withdrawal.

Examples at Different Spending Levels

Someone spending $50,000/year needs $1,250,000 to retire comfortably.

The Savings Rate Impact

FIRE success depends far more on your savings rate (the percentage of take-home income you save) than on your income. Two people earning $60,000 and $200,000 who both save 40% reach financial independence in the same number of years, because the higher earner's FIRE number is proportionally bigger.

The reason is that a savings rate does two things at once: it adds to the portfolio and it shrinks the target. Cut spending by $10,000 and you save $10,000 more per year and knock $250,000 off the number you are chasing. A $10,000 raise only does the first.

Formula: starting from zero, with a real (after-inflation) return of r and a savings rate of s, the years to a 25× target are

n = ln(1 + 25r × (1 − s) / s) ÷ ln(1 + r)

Run at a 5% real return — roughly what a stock-heavy portfolio has delivered after inflation, not the 8% nominal figure people usually quote — that produces:

Someone saving 50% of income reaches FI in about 17 years — age 42 if they start at 25. Someone saving 10% takes about 51 years, which is a normal career, not early retirement.

Note how brutally non-linear this is. Going from 10% to 25% buys back 19 years. Going from 50% to 65% buys back only six and a half. The cheap wins are all at the bottom of the table.

The 75% savings rate example:

• Income: $100,000
• Spending: $25,000 (25%)
• Savings: $75,000 (75%)
• FIRE number (25 × $25,000): $625,000
• At a 5% real return, $75,000/year reaches $610,650 after 7 years and crosses $625,000 about seven weeks into year 8
• Result: FI at 32 if they started at 25

This is why FIRE emphasizes cutting spending — a dollar not spent works both sides of the equation.

Calculation: Years to FI

Use the compound interest formula:

FV = PV × (1 + r)^n + PMT × [((1 + r)^n - 1) / r]

Where:

• FV = Future value (FIRE number)
• PV = Current savings
• r = Annual real return (5% = 0.05 — use a real return so the target stays in today's dollars)
• n = Years
• PMT = Annual savings

Example: Age 30, $100,000 already saved, spends $40,000/year, saves $80,000/year, target FI number $1,000,000.

• $1,000,000 = $100,000 × (1.05)^n + $80,000 × [((1.05)^n − 1) / 0.05]
• Solving for n: 8.7 years — FI at 39, a few months before their 39th birthday

Change the return assumption and the answer moves less than you would expect: at 7% real it is 8.0 years, at 3% real it is 9.5 years. Change the savings rate and it moves a lot. That asymmetry is the whole argument of the FIRE movement. To solve for your own numbers rather than these, work out your years-to-FI in the FIRE calculator, and if you want to see what a single extra year of contributions does to the end balance, run the same figures through the compound interest calculator.

Cost of Living Arbitrage

FIRE relies on spending less. Common strategies:

1. Geographic arbitrage: Live in a low cost-of-living city (save more) or retire abroad.

Example: Earn $100,000 in San Francisco (cost of living = $80,000/year), save $20,000. Move to a city where cost is $40,000, now saving $60,000/year.

2. Lifestyle inflation resistance: Increase income without increasing spending.

Example: Raise from $70,000 to $100,000, but keep spending at $50,000 (instead of raising to $75,000). Extra $30,000 goes to savings.

3. Housing optimization: Buy a home (reduce housing cost over time via paid-off mortgage) or rent strategically.

Early Retirement and Healthcare

A critical consideration: healthcare before Medicare eligibility at 65. Retire at 45 and that is a 20-year gap with no employer plan behind you.

Unsubsidized individual coverage on the ACA Marketplace runs several hundred to well over a thousand dollars a month depending on age, state and plan tier — and it gets more expensive every year you age, because Marketplace premiums are age-rated.

But the sticker price is usually not what an early retiree pays, and this is the single most under-appreciated fact in FIRE planning. Marketplace premium tax credits are tested on modified adjusted gross income, not on wealth. A retiree with a $1,200,000 portfolio who lives on Roth withdrawals, cash savings, and the return-of-basis portion of taxable-account sales can show a genuinely low MAGI and qualify for a substantial credit. Someone with the identical portfolio who funds the same lifestyle out of a traditional IRA reports every dollar as income and may qualify for nothing.

The planning consequence: where you draw from matters as much as how much you have. Build the taxable and Roth buckets during accumulation specifically so you have low-MAGI dollars to spend between retirement and 65. Check the current year's tables on healthcare.gov before you commit — Congress has changed the credit schedule repeatedly, and a plan built on last year's rules is a plan built on nothing.

Example: FIRE spending calculation.

• Housing: $15,000
• Food: $6,000
• Transportation: $3,000
• Healthcare: $12,000 (premiums plus out-of-pocket, assumed unsubsidized)
• Other: $4,000
• Total: $40,000 → FIRE number at 25× = $1,000,000

That $12,000 healthcare line is 30% of the budget and $300,000 of the FIRE number all by itself. If careful MAGI management cuts it to $5,000, the FIRE number falls to $825,000 — the same effect as saving another $175,000. Model healthcare explicitly; do not fold it into "other".

State Taxes and FIRE

Some states levy no income tax at all (Florida, Texas, Nevada, Wyoming, Tennessee, South Dakota, Alaska, New Hampshire and Washington, the last two taxing only certain investment income). Others have steeply graduated rates.

Be careful with the headline rate. California's 13.3% and New York's 10.9% are top marginal rates that apply to income in the millions — they are not what a FIRE household withdrawing $40,000 a year pays. Run a $40,000 withdrawal through California's graduated schedule after its standard deduction and personal exemption credit and the effective state rate lands closer to 2%, not 13%. Quoting the top marginal rate against a modest retirement income overstates the state tax bill by a factor of six or more, and that error has sent people moving across the country for a saving that was never there.

Example: retire on $40,000/year of taxable withdrawals.

• California, roughly 2% effective on that income: about $800/year of state tax → you need about $40,800 of withdrawals, a FIRE number of $1,020,000
• Texas, 0%: $1,000,000

The honest difference is around $20,000 of required portfolio, not $154,000. Where geography genuinely moves the needle for FIRE is cost of living — housing above all — and that gap is far larger than any income tax difference. The Bay Area versus a mid-size inland city is a $20,000–$40,000 swing in annual spending, which is $500,000–$1,000,000 off the FIRE number.

Two state-tax details that do matter at FIRE income levels: several states exempt some or all retirement-plan and pension income regardless of the headline rate, and Roth withdrawals are untaxed by every state, because states tax income and a qualified Roth distribution is not income.

Sequence of Returns Risk

Reaching your FIRE number is one thing; sustaining it through market downturns is another.

The sequence of returns risk is the danger that your first years of retirement coincide with a market crash.

Scenario A: Retire at 40 in 2007 (pre-financial crisis), markets crash 50% in 2008–2009.

Your $1,000,000 drops to $500,000 while withdrawing $40,000/year. Portfolio may not recover.

Scenario B: Retire at 40 in 2010 (post-crisis), markets soar. Same withdrawals are sustainable.

Mitigation:

• Keep 2–3 years of expenses in cash or short-term bonds, so a bad year never forces you to sell equities at the bottom.
• Use a flexible withdrawal rate — cutting spending 10–20% in the two worst years of a downturn rescues most portfolios that would otherwise fail.
• Compare the withdrawal rate to your real expected return, not the nominal one. A 4% withdrawal against a 5% real return leaves a 1% buffer, not the 4% you get by subtracting 4 from a nominal 8. Inflation is not free money.

Alternative Withdrawal Rates for FIRE

Some FIRE practitioners use 3.5% or 3% withdrawal rates for extra safety:

• 3.5% rule: FIRE number = spending × 28.6
• 3% rule: FIRE number = spending × 33.3

A 3.5% rule means $35,000 of annual spending requires $1,000,000, not the $875,000 that 4% would imply.

Be honest about what those rates are and are not. Nobody has "proved" a 100% success rate for anything. The published success percentages come from backtests against a single country's market history, mostly US stocks and bonds since 1926 — a period that contains the best-performing large equity market of the twentieth century. A lower rate buys margin against the possibility that the future is worse than that record; it does not buy a guarantee.

Choose based on your:

• Flexibility: willing to cut spending 10–20% in bad markets? (3.5–4% is defensible.)
• Portfolio: 100% equities has higher expected return and a far worse worst case. A 60/40 or 75/25 mix historically survived more sequences at 4% than either extreme.
• Time horizon: 30 years (4% was designed for exactly this). 40–55 years — a 40-year-old retiree — pushes toward 3–3.5%.
• Other income you can count on: a pension, rental income or Social Security at 62–70 shortens the years the portfolio has to carry alone, which is worth more than a quarter-point on the withdrawal rate.

Social Security and Pension Delay

FIRE often means retiring before Social Security (age 62) and pensions (age 55+). This creates a gap.

Example: Retire at 40, Social Security at 62, pension at 55.

• Ages 40–55 (15 years): Live on portfolio alone.
• Ages 55–62 (7 years): Live on portfolio + pension.
• Ages 62+: Live on portfolio + pension + Social Security.

Your portfolio withdrawal rate can decrease over time as these income sources kick in. This is advantageous.

Calculation example:

• Ages 40–55: Withdraw 5% ($50,000/year from $1,000,000).
• Ages 55–62: Withdraw 2% (pension covers the rest).
• Ages 62+: Withdraw 0% (Social Security + pension cover it).

This "bucketing" approach lets a smaller portfolio support early retirement if other income sources are delayed.

Occupational Pensions and FIRE

Some occupations have defined benefit pensions (police, military, teachers, some government employees). If you have one, it is almost certainly the largest single asset in your FIRE plan and the one least likely to appear in your spreadsheet — price it before anything else, using the military retirement calculator or the teacher pension calculator as applies.

A $30,000/year pension dramatically reduces your FIRE number.

Example: Retire at 55 with a $30,000/year pension.

• Spending needs: $40,000/year.
• Pension: $30,000.
• Gap from portfolio: $10,000.
• FIRE number needed: $10,000 / 4% = $250,000.

Without a pension, you'd need $1,000,000. The pension saves $750,000 in required savings.

One caveat that quietly eats a third of that advantage: most private-sector pensions are not indexed to inflation. A $30,000 pension starting at 55 still pays $30,000 at 75, by which time 3% inflation has cut its purchasing power to about $16,600. Federal (FERS), military and many state and local plans do carry a cost-of-living adjustment; check yours before you treat the pension as a permanent floor. If it is not indexed, size the portfolio to cover the erosion, not just today's gap.

What the 4% Rule Doesn't Cover

The 25× number is a starting point, not a plan. Four things it silently assumes:

1. A 30-year retirement. That is what the original research tested. A 40-year-old planning to 90 needs 50 years of survival, and the failure rate rises sharply past year 30 for exactly the reason sequence-of-returns risk exists.

2. No taxes. The 4% is a gross withdrawal. Money coming out of a traditional 401(k) or IRA is ordinary income. If a third of your portfolio is pre-tax, your spendable 4% is not 4%. Roth and taxable-basis dollars come out cleaner, which is why the account mix matters as much as the total.

3. No fees. The backtests use index returns. A 1% advisory fee on top of a 4% withdrawal is functionally a 5% withdrawal, and that is well outside the range the research supports.

4. Constant, inflation-adjusted spending. Real retirements are lumpy: a roof, a car, a parent needing care, a child's tuition. Retirees also tend to spend more in the first decade ("go-go years") and less later. Neither shape looks like the smooth line the rule assumes.

It also ignores the biggest variable of all — you might work again. A single year of part-time income at 45 does more for portfolio survival than any withdrawal-rate refinement, because it removes a year of withdrawals and a year of sequence risk at the point where the portfolio is most fragile.

FAQ

Is the 4% rule still valid in 2026?

It remains the right starting estimate and the wrong final answer for anyone retiring early. William Bengen's 1994 study and the 1998 Trinity study both tested 30-year retirements of US stocks and bonds; neither tested the 45–55 year horizon a 40-year-old faces. For a retirement longer than 30 years, most practitioners drop to 3–3.5%, which raises the multiple from 25× to between 28.6× and 33×. On $50,000 of spending that is the difference between a $1,250,000 target and a $1,650,000 one — roughly four extra working years at a 50% savings rate.

Should I count home equity in my FIRE number?

No, unless you actually intend to sell or borrow against it. Your house does not pay the electricity bill. A paid-off home helps enormously on the spending side — it removes rent or a mortgage payment from the annual figure, and every $12,000 of housing cost you eliminate cuts $300,000 off the FIRE number at 25×. But counting the equity as a portfolio asset and then also living in it double-counts. If downsizing is genuinely part of the plan, count only the expected net proceeds, after selling costs and the price of the replacement home.

What happens if the market crashes the year after I retire?

This is sequence-of-returns risk, and it is the main way FIRE fails. The defence is not prediction, it is structure: hold 2–3 years of spending in cash or short-term bonds so you are never forced to sell equities at the bottom, and be willing to cut discretionary spending 10–20% in a bad year. Flexible withdrawals do more for survival odds than any asset-allocation tweak. A retiree who trims spending in the two worst years of a downturn converts most 4% failures into successes.

How do I get health insurance before 65?

Through the ACA Marketplace, a spouse's employer plan, COBRA for up to 18 months after leaving a job, or a part-time job that offers benefits. The important mechanic is that Marketplace premium tax credits are tested on modified adjusted gross income, not on assets — so how you fund your spending changes the price. Roth withdrawals, cash, and the return-of-basis portion of a taxable sale keep reported MAGI low; traditional IRA and 401(k) withdrawals do not. Build the low-MAGI buckets during accumulation if you intend to retire before 65.

Does Social Security change my FIRE number?

Yes, substantially, and most FIRE calculations ignore it. Benefits start as early as 62, and even a reduced benefit permanently removes a chunk of the withdrawal the portfolio has to fund. If Social Security will eventually cover $20,000 of a $40,000 budget, the portfolio only has to carry the full load for the years before it starts, then half the load forever after. Check your actual estimate on ssa.gov rather than guessing — early retirement means fewer years of covered earnings, and the benefit formula averages your highest 35 years, filling any short years with zeros.

Sources

• Bengen, William P. "Determining Withdrawal Rates Using Historical Data." Journal of Financial Planning, October 1994 — the origin of the 4% rule.
• Cooley, Philip L., Carl M. Hubbard and Daniel T. Walz. "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable." AAII Journal, February 1998 — the Trinity study.
• Social Security Administration, ssa.gov — earliest claiming age, the 35-year benefit formula, and your personal benefit estimate.
• HealthCare.gov — current-year premium tax credit eligibility and the MAGI definition used to test it.
• Board of Governors of the Federal Reserve System, Survey of Consumer Finances — household savings and net worth distributions.