Free FIRE Calculators That Show Their Own Maths

The projection chart

The green line is your projected balance in today’s dollars; the dashed orange line is the target. The dot is the year they meet.

When the assumptions turn out worse

Every projection here rests on one set of inputs. These four rows re-run the page with harsher ones, because the gap between them is the real answer.

Year by year

The defaults, and the reasoning behind them

Three inputs decide almost everything here. Change all of them — that is the point of publishing them.

Investment growth: 7% nominal

Seven percent is the rough long-run return of a global equity index before costs, and the figure most FIRE spreadsheets open with. It is an average across decades, not a promise about any one decade: a portfolio holding bonds belongs lower, and anyone within five years of quitting should read the scenario rows above rather than trust a single line. Crypto holdings need their own, lower, input.

Inflation: 2.5%

Central-bank targets sit near 2% and lived experience since 2021 has run higher, so 2.5% is a deliberate middle. Every point of inflation you understate quietly inflates that growth figure and pulls your finish line closer than it is.

Withdrawal rate: 4%

That figure comes from the Trinity study's 30-year test. A retirement starting at 40 may run 50 years, which is why long-horizon planners often use 3.25% to 3.5%. The 4% rule was never a rule covers the research and the caveats; the money glossary defines every term used here.

The FI number formula

FI number = annual spending ÷ (withdrawal rate ÷ 100)

real return = ((1 + nominal) ÷ (1 + inflation)) − 1

balance next year = balance × (1 + real return) + annual saving

Worked example

Spend $48,000 a year and use a 4% withdrawal rate and your target is $1,200,000 — 25 times your spending. Start with $90,000 invested, add $24,000 a year and grow it at 4.39% after inflation (7% growth, 2.5% inflation) and the two lines meet in 2050 — 24 years. Move the withdrawal rate to 3.5% and the target jumps to $1,371,429, which costs you two more years; drop returns two points as well and it costs nine.

What this assumes: contributions land at the end of each year, returns are steady rather than sequenced, and every figure is pre-tax and in today’s dollars. Sequence-of-returns risk is real and this model leaves it out — that is what the scenario rows above are for.

Coast FIRE is the point where you can stop contributing. Your invested balance is already big enough that compounding alone carries it to your FI target by the retirement age you pick. You still need to cover your living costs until then, so what it buys is job choice — the freedom to take the lower-paid, saner work covered on the work & life desk — not the freedom to stop working.

The Coast FIRE arithmetic

Coast number = FI number ÷ (1 + real return)^{years until retirement}

Worked example

A 34-year-old spending $48,000 needs $1,200,000 at 60. At 4.39% after inflation over 26 years, every dollar invested today multiplies by 3.06 — so the coast number is $392,666. At $90,000 invested you are $302,666 short of it, and today's balance would grow to $275,043 on its own. Above the coast number you could stop contributing tomorrow and still land on target.

What this assumes: no further contributions after today, steady growth after inflation, no tax drag, and spending in retirement equal to spending now. If you are still adding money every year, the FI number calculator is the one you want; to see how much faster banking more would get you there, use the savings rate calculator.

Your savings rate sets your timeline because it works from both ends at once: it raises what you add each year and lowers the target you are adding towards. A raise you spend changes nothing here. A raise you bank changes everything, which is why we test the data desk.

The savings-rate arithmetic

savings rate = (take-home − spending) ÷ take-home

What this assumes: take-home is after tax and after payroll deductions; employer matches count as savings only if you add them to the amount banked. Once the rate is set, the Coast FIRE calculator shows when you could stop adding entirely.

This is the number people actually quit on, and the one most calculators ignore. It is not your FI number — it is the distance between your cash and your burn rate,, the number behind every Exit Interview episode, minus the emergency fund you refuse to touch.

The runway arithmetic

runway in months = (cash − emergency fund) ÷ (monthly costs − monthly side income)

What this assumes: costs and side income hold steady, the cash earns nothing, and health insurance is already inside your monthly costs — in the US that single line is the one that most often breaks a runway plan. Pair it with the side-hustle desk if the plan depends on that income holding up.

Questions people ask about these numbers

Methodology and limits

Nothing here is financial advice, and we take no commission on any of it. The model is deterministic: steady growth after inflation, yearly contributions, no tax. Every default is a stated convention, not a recommendation — change them. Full methodology.

Limits of these four models

Tax, sequence risk, a mortgage ending mid-retirement, one partner stopping before the other, a market dropping 30% in your first year out. Each moves the answer by years and none fits a six-input form, which is why the research desk takes them properly.

• What Coast FIRE actually buys you, in years
• The savings-rate number that matters more than your salary
• The 4% rule was never a rule
• Money glossary: every term used on this page