How the FIRE Calculator Works
FIRE — Financial Independence, Retire Early — comes down to one question: how big does your portfolio need to be before it can pay for your life, and how long will it take you to get there? This calculator answers both, using your own spending, savings and assumptions, and keeps every figure in today's money so the numbers mean something.
1. Your FIRE number
Your FIRE number is your yearly retirement spending divided by a safe withdrawal rate — the share of your portfolio you plan to take out each year.
FIRE number = annual retirement spending ÷ withdrawal rate
At 4% → 25 × spending · at 3.5% → ≈ 28.6 × · at 3% → ≈ 33.3 ×
The 4% rule comes from research on 30-year retirements. Retiring in your 30s or 40s can mean 50 years or more of withdrawals, which is why the calculator defaults to 3.5% — and why many early retirees plan around 3%.
2. Years to financial independence
Each year, your portfolio grows by its real (after-inflation) return and you add what you save. The year it reaches your FIRE number is your financial-independence age.
Real return = (1 + expected return) ÷ (1 + inflation) − 1
Next year's portfolio = this year's × (1 + real return) + yearly savings
Using the real return means your savings and your FIRE number both stay in today's buying power. The "future money" figure shows what the same target looks like with inflation added back in.
3. Coast FIRE
Coast FIRE is the amount that, left alone, would grow into your full FIRE number by your traditional retirement age. Hit it and you could stop investing, earning just enough to cover today's bills.
Coast number = FIRE number ÷ (1 + real return)years until traditional retirement
Why your savings rate matters most
Your savings rate does two jobs at once: it sets how much you add each year and how much you've shown you can live on. That's why the savings-rate table moves so dramatically — going from saving 20% to 50% of your income can cut decades off the timeline. For a fuller walk-through, read What Is FIRE — and Is It Realistic?, then use the Budget Planner to find room in your spending.
What this calculator doesn't model
- Taxes on withdrawals and investment growth, which vary by country and account type.
- Sequence-of-returns risk — a bad market in your first years of retirement hurts more than the same drop later.
- Pensions, state benefits or rental income that may reduce what your portfolio has to cover.
- Big one-off costs such as healthcare, children's education or a home purchase.
Frequently Asked Questions
How do I calculate my FIRE number?
Divide the amount you expect to spend each year in retirement by your safe withdrawal rate. At a 4% withdrawal rate that is the same as multiplying your annual spending by 25; at 3.5% it is about 28.6 times; at 3% it is about 33.3 times. If you expect to spend 40,000 a year, your FIRE number is 1,000,000 at 4%, about 1,143,000 at 3.5% and about 1,333,000 at 3%.
Is the 4% rule safe for early retirement?
The 4% rule comes from research on 30-year retirements using historical US market returns. Early retirees may need their money to last 40 to 60 years, so many FIRE planners use a more conservative 3% to 3.5% withdrawal rate. A lower rate means a bigger FIRE number but a smaller chance of running out of money. That is why this calculator defaults to 3.5% and lets you compare all three.
What is Coast FIRE?
Coast FIRE is the point where the money you have already invested could grow to your full FIRE number by a traditional retirement age without any further contributions. Once you reach it, you only need to earn enough to cover your current spending. The calculator shows how much you need today to coast, and the age you are on track to reach that point.
What is the difference between Lean, Fat and Barista FIRE?
Lean FIRE means retiring on a deliberately frugal budget — this calculator models it as 75% of your planned retirement spending. Fat FIRE means retiring with a more generous budget, modelled here as 150%. Barista FIRE means leaving full-time work once your investments can cover part of your spending and part-time work covers the rest; the calculator assumes part-time income covers half.
Why does this FIRE calculator use real returns?
Prices rise every year, so a FIRE number that ignores inflation is too small by the time you reach it. The calculator converts your expected return into a real (after-inflation) return and shows every figure in today's money, so the numbers keep the same buying power. It also shows what your FIRE number would look like in future money at the age you reach it.
Disclaimer: This calculator is an educational tool. Its projections assume a steady return every year, which real markets never deliver, and they don't account for taxes, fees or your personal circumstances. It is not financial advice — consider speaking with a qualified financial adviser before making retirement decisions.