01 · The number
What is a FIRE number?
Your FIRE number is the size of the invested portfolio that can pay for your life without a paycheck. The calculator uses the standard formula: FIRE number = annual spending ÷ withdrawal rate. At a 4% withdrawal rate that is 25 times what you spend in a year, so $50,000 of spending needs $1.25 million and $40,000 needs $1 million.
Two details matter more than they look. First, the target is set by spending, not income: a raise moves your FIRE number only if your lifestyle rises with it. Second, the spending figure should be what you will spend in retirement, including taxes on withdrawals and any health insurance you now get through work, minus costs that will be gone by then, like a paid-off mortgage. For a longer walk-through, read the FIRE number formula explained in plain English.
Once the target is set, the time it takes to get there comes down to three things: what you have invested today, how much you add each year, and what those investments earn. The calculator compounds monthly, adds your savings every month, and stops the clock the month your portfolio crosses the target.
02 · The withdrawal rate
The 4% rule, and what it doesn't promise
The 4% figure comes from 1990s research on US retirements, most famously William Bengen's 1994 paper and the Trinity study that followed. They asked how much a retiree could withdraw in the first year, then raise with inflation every year after, without running out of money over 30 years. Using historical returns, a starting rate around 4% held up through almost every 30-year stretch for a portfolio weighted toward stocks.
That is a useful rule of thumb, with limits worth knowing before you lean on it:
- Early retirements are longer. A 45-year retirement is well past the 30 years the studies tested. Many people planning one use 3.5% for extra margin.
- Order of returns matters. A market drop in your first few years of retirement does more damage than the same drop later, because you are selling while prices are low.
- It is history, not a guarantee. The rule describes past US markets. Future returns can be lower.
- Flexibility is the real safety net. Trimming spending after a bad year, or earning a little on the side, protects a plan more than any single percentage.
Set the withdrawal rate to 3.5% above and watch the target move: at $50,000 of spending it rises from $1.25 million to about $1.43 million. Our guide to the 4% rule goes deeper.
03 · The lever
Why your savings rate matters more than your income
Savings rate works on both sides of the equation. Every dollar you don't spend is a dollar invested, and it is also a dollar you won't need to replace in retirement. That is why two people with very different salaries reach financial independence on roughly the same schedule if they save the same share of their take-home pay.
| Savings rate | Years to FI |
|---|---|
| 10% | 50+ |
| 20% | 35.9 |
| 30% | 27.4 |
| 40% | 21.2 |
| 50% | 16.3 |
| 60% | 12.2 |
| 70% | 8.7 |
| 80% | 5.5 |
The biggest gains come from the first increases: going from 20% to 40% saves about 15 years, while going from 60% to 80% saves about 7. Anything you have already invested shortens every row. In this calculator, savings rate is take-home income minus spending, divided by take-home income. More on this in savings rate for FIRE: the fastest path to freedom.
04 · The flavors
Lean, Fat, Coast and Barista FIRE
FIRE is not one target. The same formula gives very different numbers depending on the life you plan to fund and whether you plan to stop working entirely.
Lean FIRE
Retiring on a tight budget that covers the essentials. It is the fastest route, but it leaves less room for surprises. The calculator shows a Lean target at 70% of your current spending as a rough guide; your real Lean number is whatever your essentials cost.
Fat FIRE
Retiring with room for travel, a bigger home, or generosity. It takes longer and the target is larger, but the plan has more slack to absorb bad years. The calculator shows it at 150% of your spending. See Lean FIRE vs Fat FIRE for how the two compare.
Coast FIRE
You have invested enough that, with no further contributions, growth alone will carry you to your FIRE number by a traditional retirement age. From then on, your paycheck only has to cover today's expenses. The Coast number is your FIRE number divided by (1 + return) raised to the number of years until that age. Read how Coast FIRE works and who it suits.
Barista FIRE
You leave full-time work early and cover part of your spending with part-time income, often a job that also provides health insurance. Your portfolio only has to fund the gap, so the target is (spending − part-time income) ÷ withdrawal rate. With $50,000 of spending and $20,000 of part-time pay, the 4% target falls from $1.25 million to $750,000. To model it here, enter only the gap as your spending. More in Barista FIRE: pros, cons and how to start.
05 · The inputs
How to use this calculator
- Current age. Used to turn years into the age you reach FI.
- Take-home pay. What you are paid per year after tax. If money goes to a 401(k) or IRA before it reaches your account, add it here, since it is part of what you save.
- Spending. What you spend in a year. Use the last 12 months of actual spending rather than your budget. Annual and irregular costs, like insurance premiums, car repairs and gifts, are the easiest to miss.
- Invested savings. Retirement accounts, brokerage accounts and cash set aside to invest. Leave out your emergency fund and home equity unless you plan to sell.
- Expected real return. The return after inflation. The default is 5%. US stocks have historically done better than that, but future returns may be lower, and bonds pull the average down.
- Withdrawal rate. 4% is the usual starting point; 3.5% adds a margin of safety for a long retirement.
Everything is in today's dollars, so the FIRE number you see is in the same money you spend now. The link in your address bar updates as you type, so you can bookmark a scenario or share it.
This is a model, not a forecast. It assumes steady returns, leaves out Social Security and pensions, and treats your spending as flat after inflation. Use it to see which inputs move your date the most, then revisit it as your numbers change.