How to Calculate Your FIRE Number (2026 Guide)

FIRE Number = Annual Expenses ÷ Safe Withdrawal Rate

If you’ve spent any time around the personal-finance internet, you’ve run into the term FIRE — Financial Independence, Retire Early. The idea sounds intimidating: accumulate enough money that you can stop working forever. The math, however, is shockingly simple. You can express the entire framework in a single formula and apply it to your own life in about ten minutes.

This guide walks through that math from first principles. We’ll cover where the formulas come from, the assumptions baked into them, the four common variants of FIRE you’ve probably seen (“Standard,” “Lean,” “Coast,” “Barista”), and — equally important — the things the math quietly leaves out. Two live calculators are embedded inline so you can plug in your own numbers as we go.

By the end, you should be able to compute your own FIRE number, your time-to-FIRE on current contributions, and have an honest sense of how much margin to keep against the assumptions being wrong.

FIRE number vs FI number: are they the same?

Yes. “FI number” (your financial-independence number) and “FIRE number” refer to the same figure: the portfolio that covers your annual expenses indefinitely at a safe withdrawal rate. “FI” emphasizes the independence; “FIRE” adds the retire-early intent. The arithmetic — annual expenses ÷ safe withdrawal rate — is identical either way. So if you searched for how to calculate your FI number, everything below applies unchanged.

Part 1: The core formula

The whole FIRE framework is built on two ideas. The first is a rule of thumb about how much money a portfolio can sustainably distribute each year. The second is compound growth, which lets you turn a sum invested today into a much larger sum decades from now.

The FIRE number

Your FIRE number is the portfolio size that, at a “safe” withdrawal rate, covers your annual expenses indefinitely. The formula is intentionally crude:

FIRE Number = Annual Expenses ÷ Safe Withdrawal Rate

At a 4% withdrawal rate (a common default we’ll dissect in a moment), this collapses to “25 times your annual expenses.” Spend $40,000 per year? Your FIRE number is $1,000,000. Spend $80,000? It’s $2,000,000. The relationship is linear: every $1 of recurring annual spending requires about $25 in invested assets to fund forever.

The withdrawal rate is the lever. At 3.5% you need ~28.6× expenses; at 3% you need ~33×; at 5% you need only 20×. Lower rates buy more safety margin — the portfolio is more likely to survive a long retirement — at the cost of needing a much bigger portfolio.

FIRE number by annual spending

The full table for common US-household expense levels, at each commonly cited safe withdrawal rate:

The middle two columns are the most commonly used for early-retirement planning, where horizons exceed 40 years and the original Trinity 30-year framing doesn’t fully apply.

Where the 4% rule comes from

The 4% rule is shorthand for two pieces of research. The first is William Bengen’s 1994 paper “Determining Withdrawal Rates Using Historical Data”, which tested the maximum percentage a retiree could withdraw — adjusted upward for inflation each year — without running out of money over a 30-year retirement. Bengen found that with a 50–75% stock allocation, 4% was historically safe.

The Trinity Study (Cooley, Hubbard, Walz, 1998) re-ran similar tests with broader portfolio mixes and confirmed the result: a portfolio of 50–75% stocks with a 4% inflation-adjusted withdrawal had a very high success rate over 30 years.

That’s it. That’s the whole “rule.” It’s not a law of physics; it’s a historical observation about a specific country (the US), a specific period (mostly the 20th century), and a specific time horizon (30 years).

Three caveats matter for FIRE pursuers:

1. The horizon is 30 years. If you retire at 40 expecting to live to 90, you’re planning for a 50-year window. Bengen and Trinity say nothing directly about that — and longer windows are historically less forgiving.
2. The data is mostly US. Globally diversified portfolios show somewhat lower safe rates because not every market produced US-style 20th-century returns.
3. It assumes you stick to the plan. The 4% rule is a static withdrawal: each year you take out 4% of your initial portfolio plus inflation. In practice, most retirees adjust based on how the portfolio is doing.

A widely quoted modern adjustment is to target 3.25–3.5% for very long retirements. That translates to a 28.6–33× expense multiple. The calculator below lets you choose; the default of 4% is a reasonable starting point.

Time to FIRE: compound growth meets contributions

The second piece of the math answers: how long until I get there? Given a starting balance, a monthly contribution, and an expected real return, the closed-form solution for the number of months to reach a target is:

Months = log((Target + C/r) ÷ (Starting + C/r)) ÷ log(1 + r)

where C is your monthly contribution and r is the monthly real return. This is just the future-value-of-an-annuity formula solved for time.

You don’t need to compute this by hand. Plug your numbers into the calculator below and watch how each lever — contributions, return, expenses, withdrawal rate — moves the date.

What age can you reach FIRE? (Your FIRE age)

Your FIRE age is simply your current age plus your years to FIRE. What surprises most people is what controls it: not salary, but savings rate. A higher savings rate works on both sides of the equation at once — it raises the amount flowing into the portfolio and lowers the expense base your FIRE number is computed from. That’s why two households with very different incomes but the same savings rate reach FIRE on roughly the same timeline.

The table below assumes you’re saving from a $0 start, earning a 5% real return, and targeting a 4% withdrawal rate:

Read the right column as an offset from your current age. A 30-year-old saving 50% of after-tax income reaches FIRE around age 47. The same person at a 10% savings rate lands at or past traditional retirement age anyway — the portfolio arrives roughly when a conventional career would have ended. Moving from 20% to 50% cuts about twenty years off the timeline, which is why savings rate, not income, is the variable worth optimizing.

Two adjustments to the baseline. If you already have a portfolio, the years shrink — the Coast FIRE number by age table shows what a head start is worth at each age. And to find where you sit in the table above, the savings rate calculator computes your own rate from income and spending.

Part 2: Try it on your own numbers

This is the Standard FIRE calculator. Inputs are on the left; the FIRE number, time to FIRE, and projection at 65 update in real time. All math runs in your browser.

A few quick experiments worth doing now:

• Lower your assumed real return from 7% to 5%. Notice how time-to-FIRE jumps. Real returns are the single most leveraged assumption.
• Drop your withdrawal rate from 4% to 3.5%. Your FIRE number grows by ~14%; your time-to-FIRE grows similarly. Lower SWR is a real cost.
• Raise your annual contribution by $5,000. This usually shaves several years off the date — high savings rate beats high income.
• Cut $5,000 off retirement expenses. This usually shaves more years off than adding $5,000 of contributions, because lower expenses cut both the target and the time to reach it.

The single most important number in this calculator isn’t your FIRE number. It’s your savings rate — the fraction of after-tax income you save and invest. A higher savings rate compounds in two directions: it means more money flowing in, and it means you’ve already learned to live on less, which lowers your future FIRE number.

Part 3: The four flavors of FIRE

The same underlying math powers every variant of FIRE you’ve seen. The flavors differ in which expense level goes into the formula and what “retirement” actually looks like.

Standard FIRE

What we just calculated above. Stop working today, draw down a portfolio that covers typical middle-class expenses ($50–80k/yr for an individual or couple, depending on geography). The classic 25× target.

This is the most ambitious version of FIRE — you fully sever the dependency on employment income — and the latest milestone. Most people doing Standard FIRE in their 40s have been saving aggressively (50%+ savings rate) for over a decade.

Lean FIRE

Same math; smaller expenses. Lean FIRE typically means $25,000–40,000/yr for an individual or $40,000–55,000/yr for a couple. The portfolio target shrinks proportionally — at $30,000/yr expenses and a 4% rate, the Lean FIRE number is $750,000.

The trade-off is lifestyle. Lean FIRE is reachable years sooner than Standard FIRE — often in the 30s rather than 40s — but only works if you can durably live on a lean budget. Geographic arbitrage (low cost-of-living areas, or moving abroad to countries with cheaper healthcare) makes Lean FIRE far more viable.

The big risk Lean FIRE practitioners under-discuss is lifestyle drift. Living on $30k at 30 is different from living on $30k at 50. Many Lean FIRE retirees eventually drift toward Barista FIRE (part-time work to top up) or Standard FIRE (more saving) as life circumstances change.

Open the Lean FIRE calculator →

Coast FIRE

Coast FIRE is the smallest of the four targets and arguably the most useful waypoint. It answers a different question: not “how much do I need to retire today?” but “how much do I need today so that compound growth alone gets me to Standard FIRE by retirement age, even if I stop saving?”

The math:

Coast FIRE Number = FIRE Number ÷ (1 + r)^n

where r is your real return and n is years until retirement. At 7% real for 35 years, the multiplier is ~10.7×: every dollar invested today becomes ~$10.70 of retirement spending power.

Concretely: a 30-year-old planning to retire at 65 on $40,000/yr (FIRE number $1,000,000) needs roughly $93,500 invested today to coast — even if they never add another dollar to their portfolio.

The reason Coast FIRE matters is optionality. Hitting it doesn’t force you to quit your job. What it changes is the relationship: income from work goes from “necessary to retire on time” to “necessary only to cover your current expenses.” You can downshift, switch to a job you actually enjoy, take a sabbatical — without setting your retirement date back.

Try the Coast FIRE calculator with your numbers:

For most working professionals in their 30s, Coast FIRE is meaningfully closer than Standard FIRE — often by a decade. It’s worth knowing the number.

Barista FIRE

Barista FIRE is the hybrid: your portfolio covers part of your expenses, and a part-time job covers the rest. The name comes from a US-specific quirk — Starbucks and a few large employers offer healthcare benefits to part-time staff — but the principle generalizes.

The math adjusts the formula: only the gap between expenses and part-time income needs to be covered by the portfolio.

Barista FIRE Number = (Annual Expenses − Part-time Income) ÷ Safe Withdrawal Rate

At $50,000/yr expenses and $20,000/yr part-time income, the Barista FIRE number is $750,000 — versus $1,250,000 for full Standard FIRE on the same expenses. Adding $20k/yr of part-time income shrinks the required portfolio by half a million dollars, which typically translates to years of saving avoided.

Barista FIRE is often the most realistic milestone for people in their late 30s and 40s. It splits the difference: not “stop working” but “stop relying on full-time high-stress work.”

Open the Barista FIRE calculator →

Comparison at a glance

For a household spending $50,000/yr:

The right milestone depends on what question you’re actually asking. Most FIRE pursuers reach Coast first (often unintentionally), then either Barista or Standard.

Part 4: What the formulas don’t tell you

The math we’ve been doing is simple by design. That’s a feature — it’s easy to verify and easy to reason about. But every simplification leaves out something real.

Sequence-of-returns risk

The 4% rule averages historical performance. In any individual retirement, what matters is not the average return but the order of returns. Hitting a 30% drawdown in your first year of retirement is far worse than hitting one in year 25 — because you’re withdrawing from a portfolio that hasn’t compounded yet. This is “sequence-of-returns risk,” and it’s the single biggest reason actual retirements fail more often than the historical math suggests.

Mitigations include holding 1–2 years of expenses in cash or short bonds (so you don’t sell stocks at the bottom), starting with a slightly lower withdrawal rate, and using a “guardrails” approach where you cut spending if the portfolio drops below a threshold.

Real returns and inflation

Every formula in this guide uses real (after-inflation) returns. If you input nominal expectations like “the S&P 500 returns 10% per year,” your math will be wrong by ~2.5–3 percentage points (the historical inflation rate).

The conventional baseline is 6–8% real for a globally diversified equity portfolio. Lower it if you hold significant bonds or cash. Lower it further if you want a conservative buffer.

Annual expenses should also be in today’s dollars. Don’t try to “inflate” them forward yourself; the model handles that implicitly through the real-return assumption.

Taxes

The 4% rule, as classically stated, is pre-tax. Once you actually withdraw, location matters: traditional 401(k) and IRA withdrawals are taxed as ordinary income; Roth withdrawals are tax-free; taxable account withdrawals trigger capital gains. A common simplification is to add 10–15% headroom to your FIRE number if most of your savings are pre-tax.

For early retirees in the US, the Roth conversion ladder is a legendary tax-arbitrage technique: convert traditional IRA dollars to Roth in low-income years, pay minimal tax, and access the converted principal tax-free after a five-year window.

Healthcare (US-specific)

For US-based early retirees, healthcare is often the deciding variable. The math usually depends on ACA subsidies, which most lean and barista FIRE retirees qualify for (income below ~400% of the federal poverty line). If ACA subsidies are politically reduced or eliminated, the cost picture changes significantly.

Outside the US — most of Western Europe, Canada, Australia, and many other countries — universal healthcare makes early retirement much more straightforward, and FIRE math at the same expense level is significantly more conservative.

Lifestyle creep

The most underappreciated risk in any FIRE plan is that today’s $50k lifestyle won’t be tomorrow’s $50k lifestyle. Aging tends to push expenses up — healthcare, comfort, family. Career success tends to push them up too. A FIRE number computed on today’s spending without any cushion can become tight a decade later.

Common adjustments: target 1.2–1.3× your strict FIRE number, or model scenarios with 10% higher expenses to see how the date moves.

Behavioral risk

Markets test discipline. The biggest single thing that separates successful long-term investors from unsuccessful ones is whether they sell during drawdowns. A FIRE plan that requires precise execution during a 40% bear market — without panic-selling, without changing strategy — is a plan that depends on discipline, not just math.

This isn’t fixable with formulas. It’s fixable by automating contributions (so you don’t get to decide month-to-month), keeping a written investment policy statement you re-read during volatility, and having an emergency cash buffer so you never have to sell stocks.

Part 5: How to actually make progress

Computing your FIRE number is the easy part. Reaching it is the work. A few principles that consistently matter:

Track savings rate, not net worth. Net worth bounces around with markets and is easy to fool yourself with. Savings rate (after-tax savings ÷ after-tax income) is something you control directly. Target 25%+ to begin with; 50%+ if you’re serious about early FIRE.

Increase savings rate by lowering expenses, not raising income. Lifestyle creep eats raises. Lowering recurring expenses cuts both your savings rate denominator and your eventual FIRE number — a double benefit. A $500/mo recurring expense cut today is worth $150,000 of FIRE number reduction at a 4% rate.

Use tax-advantaged accounts first. In the US, that’s 401(k) match (free money), then Roth IRA (free of capital gains), then 401(k) up to the limit, then HSA (triple tax advantage if eligible), then taxable accounts. Outside the US, the equivalents vary; the principle is universal.

Keep it boring. Index funds, dollar-cost averaging, automated contributions. The FIRE community has a strong consensus on this for a reason: complexity correlates with underperformance. Total-market or S&P 500 index funds beat ~85% of professional managers over 15-year periods.

Rebalance once a year. That’s it. More frequent rebalancing introduces tax drag without meaningful benefit.

Part 6: Putting it together

Here’s a one-page version of your FIRE plan:

1. Annual expenses in today’s dollars: __________
2. Withdrawal rate (4% default; 3.25–3.5% for very long retirements): __________
3. FIRE number (1 ÷ 2): __________
4. Current invested assets (excluding home equity): __________
5. Annual contribution (savings + employer match): __________
6. Expected real return (7% baseline; lower if bond-heavy): __________
7. Years to FIRE (use a calculator): __________
8. Coast FIRE number (3 ÷ (1.07)^years to age 65): __________
9. Buffer multiplier (1.0× minimum, 1.2–1.3× recommended): __________

If you’ve gotten this far in the guide and filled in the blanks, you have a more rigorous FIRE plan than 95% of the people who casually use the term.

The thing left to do is automate. Every dollar of friction between your paycheck and your investment account is a dollar that won’t compound. Set up direct deposit to a brokerage. Set up automatic monthly buys of a target-date or total-market index fund. Don’t look at the balance more than once a quarter. Re-read your plan once a year and adjust.

The math is simple. The execution is just patience.

Go deeper on FIRE math:

• What is a FIRE number? — the plain-language definition and a quick worked example.
• The FIRE formula — the equation itself, plus the Coast, Lean, and Barista variants.
• What is the average FIRE number? — realistic targets across spending levels.
• What is Fat FIRE? — the above-average-budget variant, and the Fat FIRE calculator for your own numbers.
• FIRE number for a $50k or $60k salary — why spending, not salary, sets the target.
• Coast FIRE number by age — the table from 25 to 45, and the discount-to-today math.
• Is $2 million enough to retire? — what a specific portfolio actually buys.
• Compound interest: the most misunderstood formula in finance — the underlying engine of every FIRE projection.
• What is the 4% rule, exactly? — where the number came from, what it assumes, and when to use 3.5% or 4.5% instead.
• Sequence-of-returns risk — why two retirees with the same average return can have very different outcomes.
• Savings rate: the one number that decides your time to FIRE — the lever that controls everything upstream.

Related calculators:

• Coast FIRE Calculator — when can you stop saving?
• FIRE Number Calculator — find your number and the year you hit it.
• Lean FIRE Calculator — minimum-viable retirement.
• Barista FIRE Calculator — portfolio + part-time income.
• Compound Interest Calculator — what time does to money.
• All calculators