What is a FIRE number?

Your FIRE number is the size of invested portfolio that lets you live off withdrawals indefinitely. It is your annual expenses divided by your safe withdrawal rate. At a 4% rate, that is 25 times your yearly spending.

How is the FIRE number calculated?

FIRE number = annual expenses divided by (withdrawal rate / 100). For example, 30,000 of expenses at a 4% withdrawal rate gives 30,000 / 0.04 = 750,000. Lowering the withdrawal rate raises the target because you are drawing a smaller slice each year.

What is a safe withdrawal rate?

It is the percentage of your portfolio you withdraw in the first year of retirement, then adjust for inflation. The 4% rule comes from the Trinity study and is a common starting point, but many people choose 3% to 3.5% for a longer horizon or a lower-return outlook.

How does my savings rate affect years to independence?

Savings rate is the single biggest lever. A higher rate both shrinks the spending you need to cover and grows your portfolio faster, so years-to-FI fall sharply. The calculator projects your balance forward each year until it reaches the target.

What is the difference between Lean, standard and Fat FIRE?

Lean FIRE assumes a leaner lifestyle — here modelled at 70% of your stated expenses. Standard FIRE uses your actual expenses. Fat FIRE targets a more comfortable lifestyle, modelled at 150% of expenses, which needs a larger portfolio.

Should I use a real or nominal return?

Use a real (after-inflation) return, because your expenses and FIRE number are in today money. A common real-return assumption for a diversified stock-heavy portfolio is 4% to 5%. Using a nominal return would overstate how quickly you reach a target expressed in today prices.

FIRE Number Calculator

A FIRE number calculator works out the size of invested portfolio you need to reach Financial Independence, Retire Early (FIRE) — and then estimates how many years it will take you to get there. It is for anyone planning early retirement, a career break, or simply wanting a concrete savings target instead of a vague “save more” goal. Every figure you type stays in your browser; nothing is uploaded.

How it works

The tool runs in two stages. First it computes your FIRE number: the portfolio that can fund your spending forever at your chosen withdrawal rate. The formula is your annual expenses divided by the withdrawal rate, so a lower rate produces a larger target. It also shows Lean FIRE (70% of your spending) and Fat FIRE (150% of your spending) so you can see a realistic range rather than a single number.

Second, it projects your portfolio forward year by year. Each year it adds your savings — either a percentage of your take-home income or a fixed amount — and grows the whole balance by your expected real return. It keeps compounding until the balance crosses your FIRE number, then reports the exact years to financial independence, interpolating the final partial year so the answer is precise rather than rounded up. A line chart plots your projected portfolio against the target, and an optional table lists every year with its contribution, growth and end balance. The year you cross the line is highlighted.

Because the calculator uses a real return and expenses in today money, the target and the timeline are both expressed in today purchasing power — you do not have to mentally strip out inflation.

Formula note

The core relationship is:

FIRE number = annual expenses ⁄ (withdrawal rate ÷ 100)

At the classic 4% withdrawal rate this is the same as 25 × annual expenses. The year-by-year projection uses standard annual compounding: each year the new balance is the old balance plus contributions, all multiplied by one plus the real return.

Worked example

Suppose you spend 30,000 a year, plan to withdraw at 4%, and already have 50,000 invested. Your FIRE number is 30,000 / 0.04 = 750,000. Now say your take-home income is 55,000 and you save 40% of it — that is 22,000 a year — and you assume a 5% real return. Starting from 50,000, the portfolio compounds and receives 22,000 each year. It crosses 750,000 in roughly 17 years. Push the savings rate to 55% and the same target arrives several years sooner, because you both save more and need slightly less runway. Drop the withdrawal rate to 3.5% and the target rises to about 857,000, adding time. Try each lever above and watch the chart and the years-to-FI figure move.

Everything is calculated locally in your browser — no numbers are uploaded or stored on a server.