FIRE Calculator 2026

A FIRE calculator is an early retirement planning tool that estimates how much money you need to reach financial independence and when you might get there. It uses your current savings, monthly contributions, expected investment return and inflation to project the future value of your portfolio in today's dollars. Most FIRE calculators are built around the 4% rule and the "rule of 25." The calculator multiplies your desired annual spending in retirement by 25 to estimate your target portfolio size, then runs compound-growth math to see how your savings may grow over time. If your projected portfolio meets or exceeds that target by your chosen retirement age, you are considered financially independent under the model.

Your FIRE number is the size of your investment portfolio needed to cover your annual living expenses using a sustainable withdrawal rate. A common rule of thumb is the 4% rule, which says you can withdraw about 4% of your portfolio in the first year of retirement and adjust that dollar amount for inflation each year after. To calculate your FIRE number, first estimate how much you want to spend per year in retirement in today's dollars, then divide that number by 0.04 (or multiply by 25). For example, if you plan to live on $50,000 per year, your FIRE number is roughly $1.25 million. If you prefer a more conservative withdrawal rate such as 3.5%, divide your annual spending by 0.035 instead.

The 4% rule comes from historic studies of U.S. stock and bond returns that looked at whether a portfolio could survive 30 years of inflation-adjusted withdrawals. Under those assumptions, starting with a 4% withdrawal rate and increasing withdrawals with inflation almost always preserved the portfolio over a 30-year retirement, especially with 50-75% invested in stocks. However, early retirees often need their portfolio to last longer than 30 years and face sequence-of-returns risk if markets fall early in retirement. Many FIRE practitioners now treat 4% as an upper bound rather than a guarantee and use more conservative rules like 3-3.5%, dynamic spending adjustments, or flexible part-time work to reduce risk.

How much you need to save every month for early retirement depends on four main variables: your current savings, your target retirement age, your expected investment return and inflation, and your desired annual spending in retirement. A FIRE calculator uses these inputs to solve for the monthly contribution required for your portfolio to grow to your FIRE number by a specific age. In general, the more aggressively you want to accelerate your retirement date, the higher your savings rate needs to be. Many FIRE examples show people saving 50-70% of their income to reach financial independence in 10-15 years, while more moderate paths might involve saving 20-40% of income over a few decades.

A robust FIRE calculator separates nominal returns (the headline investment return) from real returns (after inflation) so that results are shown in today's purchasing power. It converts your expected long-term investment return and inflation assumption into a real growth rate and compounds your portfolio at that rate until your target retirement age. On the spending side, the calculator typically asks for your desired retirement expenses in today's dollars and assumes they will rise with inflation over time. During retirement, it models withdrawals using the chosen safe withdrawal rate and inflates the dollar amount of withdrawals each year, then compares that path to your projected portfolio value to estimate whether your plan is likely to be sustainable.