FIRE Calculator (Financial Independence)

The calculator does two steps. It turns your monthly spending into a yearly figure, then divides by the withdrawal rate you enter:

FIRE number = (monthly expenses × 12) ÷ (withdrawal rate ÷ 100)

With the defaults, $4,000 a month is $48,000 a year, and $48,000 ÷ 0.04 gives a $1,200,000 FIRE number. Dividing by a rate is the same as multiplying by its inverse, so 4% means 25 times your annual spending.

That is the whole model. The tool doesn't simulate investment returns, inflation, taxes, fees or how long the money has to last.

The field is labelled “safe withdrawal rate” and starts at 4%, but nothing in the calculator tests whether a portfolio could actually support that rate. It is the share of the portfolio you plan to take out in the first year, and choosing it is your call. Because the rate is a divisor, small changes move the target a lot. For $4,000 a month:

Running two or three rates shows you a range to plan around rather than a single target.

Enter what you expect to spend once you stop working, which may differ from today's budget:

• Drop costs that end: commuting, work clothes, a mortgage you will have paid off.
• Add costs that start: health insurance you currently get through work, more travel.
• Spread out irregular costs: replacing an $18,000 car every 6 years is $250 a month.
• Include taxes on the money you will withdraw, since the portfolio has to fund after-tax spending.
• Subtract income that continues. $1,000 a month of part-time income turns $4,000 of expenses into $3,000 for the portfolio, and the FIRE number falls to $900,000.

Each $500 a month of spending moves the target by $150,000 at 4%: $3,500 gives $1,050,000 and $4,500 gives $1,350,000.

The two extra rows are fixed multiples of your result: lean FIRE is 70% of the FIRE number and fat FIRE is 150%. At the defaults that is $840,000 and $1,800,000. They are shortcuts built into the tool, not standard definitions. A better way to size a lean or comfortable version is to write out that budget and enter it as the monthly expense.

The FIRE number is in today's dollars. If your date is years away, prices will have moved by then, so revisit the figure as you go.

To see what monthly saving reaches it, enter the FIRE number as the goal in the savings goal calculator. To see where your current saving leads, use the investment calculator.

Also check when each pot of money becomes usable. For a Roth IRA, withdrawals are tax- and penalty-free only after a 5-year period and on or after age 59½, or under a few exceptions such as disability. If you plan to stop work earlier, you may need part of the target in accounts you can reach before then.