What is FIRE and what is an FI number?
FIRE stands for "financial independence, retire early." The idea is simple: build an investment portfolio large enough that its withdrawals can pay for your spending, so work becomes a choice. The key figure is your FI number: the portfolio size at which a chosen withdrawal rate covers your yearly spending.
The formula is FI number = yearly spending ÷ withdrawal rate. If you expect to spend $40,000 a year and use a 4% withdrawal rate, your FI number is $40,000 ÷ 0.04 = $1,000,000. Spend less, or accept a higher withdrawal rate, and the number shrinks; spend more, or plan on a lower rate, and it grows.
How this calculator works
Enter your current savings, the yearly spending you expect in retirement, how much you save each year, the real return you expect and your withdrawal rate. The calculator adds your savings to the portfolio at the end of every month, lets it grow at your return, and reports how long it takes to reach the FI number. It also draws a year-by-year chart and a table of the answer at other returns and withdrawal rates.
Everything is in today's dollars. The return you enter is a real return, which means the return after inflation, so you do not need to guess a separate inflation rate: your spending and savings are treated as staying the same in purchasing power. With the default inputs ($100,000 saved, $30,000 added a year, $40,000 spent a year, a 5% real return and a 4% withdrawal rate), the portfolio reaches the $1,000,000 FI number in about 16 years and 9 months.
The 5% default is an assumption, not a forecast. Nobody knows what markets will return, and results can differ widely from year to year. That is why the table lets you test lower returns.
About the 4% withdrawal rate
A 4% withdrawal rate is a commonly used rule of thumb. It grew out of research, often called the Trinity study, that looked at historical U.S. stock and bond returns over 30-year retirement periods. It is general background, not a promise: past market data does not guarantee future results, and a plan that must last 40 or 50 years faces a longer period and the risk of poor returns early on. Some people therefore test lower rates such as 3% or 3.5%, which the table shows. The calculator does not model taxes, investment fees, Social Security, health insurance or changes in spending, all of which matter in a real plan.
Tax-advantaged accounts and early withdrawals
Retirement accounts can help you build the portfolio faster. For 2026 the IRS limit on employee contributions to a 401(k) is $24,500, plus $8,000 more from age 50 ($11,250 at ages 60 to 63), and the IRA limit is $7,500, plus $1,100 more from age 50. Traditional accounts are generally taxed when you withdraw, and Roth accounts are funded after tax. See the IRS announcement of the 2026 limits.
If you plan to retire early, remember the early withdrawal rule. Money taken from a 401(k) or traditional IRA before age 59½ is generally subject to an extra 10% tax on top of regular income tax, unless an exception applies. The IRS lists several, including death or disability, a series of substantially equal periodic payments, leaving your job in or after the year you turn 55 (workplace plans only), certain medical expenses, and limited amounts for a first home, education, birth or adoption. Roth IRA contributions, but not their earnings, can generally be withdrawn at any time. Read IRS Topic No. 557 and the IRS list of exceptions before you rely on any of them.
Ways to reach financial independence sooner
- Save more. In the early years your savings matter more than your return, so a higher yearly amount shortens the timeline the most.
- Spend less. It lets you save more and lowers the FI number you need.
- Plan for health care. If you retire before Medicare starts at 65, the cost of coverage can be a large part of your spending.
This calculator is a general math tool, not investment, tax or legal advice, and it does not predict returns. For your own money, speak with a qualified professional.
Frequently asked questions
What return should I enter?
Enter the yearly return you want to test after inflation and fees. The 5% default is only an assumption for the calculator. Because no one can know future returns, try several values: a plan that only works at an optimistic return has little room for error.
Is the 4% rule safe for early retirement?
The 4% rule is a rule of thumb based on historical U.S. data over 30-year periods, not a guarantee. If you retire in your 30s, 40s or early 50s, your money must last longer than 30 years, and a weak market early in retirement can do more damage. Many people test lower withdrawal rates; the table shows what a lower rate does to your FI number and timeline.
Does the calculator include taxes and Social Security?
No. The FI number is based on the spending you enter and the withdrawal rate, and the calculator does not estimate income tax, the 10% early withdrawal tax, investment fees or Social Security. Enter spending as the amount you need from the portfolio.