FIRE calculator

Calculate your FIRE number and years to financial independence

Math: FIRE number = annual spending ÷ (safe withdrawal rate ÷ 100). Years to FI are simulated year by year: balance = balance × (1 + real return) + annual savings, until the balance reaches the FIRE number. This is a simplified model; it does not account for taxes, Social Security, market volatility, or spending changes over time.

What is FIRE (financial independence, retire early)?

FIRE is a savings strategy built around one goal: accumulate enough invested assets that the returns alone can fund your living expenses indefinitely, so working for income becomes optional. It is not a single number or a single age; it is whatever point your own invested savings can sustainably cover your own spending. The "retire early" part is optional in practice, plenty of people reach financial independence and keep working, but the calculation is the same either way.

The strategy has two levers: how much you spend, and how much of your income you save and invest instead of spending. Because those two numbers determine both your target (higher spending needs a bigger pile) and your speed toward it (a bigger gap between income and spending means more money invested each year), the math rewards a high savings rate more than a high income.

What is the 4% rule, and what is the 25x rule?

The 4% rule comes from financial planner William Bengen's 1994 analysis of historical U.S. stock and bond returns, later expanded by the 1998 "Trinity study" (Cooley, Hubbard, and Walz). It found that withdrawing 4% of a portfolio's starting balance in year one, then adjusting that same dollar amount for inflation every year after, held up across a large majority of rolling 30-year periods in the historical data. It was built around a roughly 30-year retirement, which is why FIRE planning, which often means a retirement lasting 40 or more years, treats 4% as a starting point to stress-test rather than a guarantee (more on this below).

The 25x rule is the same idea turned around into a savings target. If a 4% withdrawal is meant to cover one year of spending, then the total portfolio needs to be 25 times that annual spending (1 divided by 0.04 equals 25). A 3.5% withdrawal rate implies about 28.6x spending; a 4.5% rate implies about 22.2x. The formula in general terms: FIRE number = annual spending ÷ withdrawal rate, where the withdrawal rate is written as a decimal (4% = 0.04).

Why does your savings rate matter more than your income?

Two things determine how many years of work stand between you and financial independence: how much of each paycheck you invest, and how large a multiple of your spending you need to accumulate. Both of those are driven by the same number, your savings rate (annual savings divided by income), which is why it dominates the calculation regardless of whether you earn $50,000 or $500,000 a year. A high earner who spends nearly everything they make reaches FIRE no faster than a modest earner who spends nearly everything they make; what changes the timeline is the gap between income and spending, not the income itself.

The table below shows years to financial independence at different savings rates, assuming a 5% real (after-inflation) investment return, a 4% withdrawal rate (25x expenses), starting from $0 already saved, and that the savings rate stays constant. It uses the same year-by-year compounding formula as the calculator above.

Computed from the 25x rule and year-by-year compounding (balance × 1.05 + annual savings each year), the same formula the calculator above uses. This style of savings-rate table was popularized by the personal-finance blog Mr. Money Mustache in "The Shockingly Simple Math Behind Early Retirement" (2012); figures here are independently calculated, not copied from that post, and will differ slightly depending on rounding and compounding assumptions.

The jump between a typical 10% to 15% savings rate (a 40-plus year timeline) and a 50% savings rate (about 17 years) is the core argument FIRE writers make for cutting spending rather than only chasing a higher income: doubling your income while keeping spending flat moves your savings rate (and therefore your timeline) far more than a raise alone, because every extra dollar saved both grows your pile and shrinks the target it needs to reach.

What are lean FIRE, coast FIRE, and fat FIRE?

These are informal community terms, not standardized financial terms, describing different flavors of the same 25x calculation:

• Lean FIRE targets a minimal, tightly budgeted spending level, often cited as under $40,000 a year for a household, which produces a smaller FIRE number (25 times a smaller spending figure) reached sooner, at the cost of little slack for discretionary spending.
• Fat FIRE targets a spending level well above typical, often $100,000 or more a year, producing a much larger FIRE number that takes longer to reach but supports a higher standard of living once there.
• Coast FIRE is different in kind: it is the savings balance at which, with no further contributions at all, investment growth alone would carry the balance to a full FIRE number by a traditional retirement age (say 65). Someone who has hit their coast FIRE number can stop saving for retirement entirely and only needs to cover current spending until then, though they typically still need to work to cover that current spending.

What are the risks and limits of the FIRE math?

The calculator above is a simplified model, and the real 4% rule research carries specific caveats that matter more for an early retirement than a traditional one.

Sequence-of-returns risk. The 4% rule was tested against roughly 30-year retirements. A market downturn in the first few years of retirement forces selling shares at depressed prices to fund withdrawals, permanently reducing the principal available to recover when the market turns around, even if the average return over the full retirement ends up fine. Two people with identical average returns can end up in very different places depending on the order those returns arrived in.

A longer horizon than the original research. Retiring at 35 or 45 asks a portfolio to last 50 or more years, well beyond the roughly 30-year periods Bengen and the Trinity study tested. Most FIRE writers and later researchers who have revisited the 4% rule for longer horizons argue for a lower starting withdrawal rate (commonly 3% to 3.5%) precisely because of this longer runway, which is why the calculator lets you adjust the withdrawal rate rather than fixing it at 4%.

Healthcare before 65. Retiring before Medicare eligibility at 65 means covering health insurance without an employer plan. This is a real, often underestimated cost in early-retirement budgets; see ACA marketplace health insurance for how that coverage and its subsidies work.

The model itself. The calculator assumes a constant real return and a constant savings rate every year, which real markets and real life do not deliver. It also ignores taxes on withdrawals and any Social Security you may eventually receive, both of which shift the true number in individual cases. Treat the output as a planning estimate, not a guarantee.

Worked example: two people, same income, different savings rates

Take two people, both age 30, both earning $80,000 a year take-home, both starting with $50,000 already invested, both assuming a 5% real return and a 4% withdrawal rate.

• Spends $50,000, saves $30,000 (a 37.5% savings rate): FIRE number = $50,000 ÷ 0.04 = $1,250,000. Reaches it in about 22 years, at age 52.
• Spends $65,000, saves $15,000 (an 18.75% savings rate): FIRE number = $65,000 ÷ 0.04 = $1,625,000, a larger target, reached with less money saved each year. That combination takes about 41 years, at age 71, nearly double the time, from the same income.

The income was identical in both cases. The nearly 19-year gap came entirely from spending less and saving more of the same paycheck.

The flat truth: it is a savings-rate problem, not an income problem

The FIRE number and the years-to-FI calculation are both just algebra, 25 times spending and a compounding formula, and neither depends on how much you earn directly. What they depend on is the gap between what you earn and what you spend. A higher income helps only to the extent it widens that gap rather than being absorbed by higher spending. The 4% withdrawal rate behind the FIRE number is a well-tested historical benchmark, not a guarantee, and it gets shakier the longer a retirement needs to last, which is exactly the case FIRE puts it in. Use the calculator to see your own number and timeline, and treat both the withdrawal rate and the projected return as assumptions to stress-test, not facts.

Related pages: how much do you need to retire? covers the 4% rule and Social Security in more depth for a traditional retirement age, which retirement account should you use? covers where to hold the savings this calculator assumes you are investing, and the compound interest calculator isolates just the growth side of this math.