How long would your money last?

Then, year by year, the way the 4% rule research set it up: your spending comes out at the start of the year, and what's left grows (or shrinks) at the real return. Everything is in today's dollars, so the same spending each year means it keeps up with inflation.

The “ceiling” is the level spending that would use up every dollar in exactly the years you chose, at a steady return. It's there to show the edge, not to aim for.

Once you're living on your savings, a fall in the first few years hurts more than the same fall later, because you're selling while prices are down. That's sequence-of-returns risk, and researchers have found the early years of retirement matter most (Pfau and Kitces, 2014 (opens in a new tab)).

The rough-start boxes let you test it: a few bad years, then your usual return. The default (three years at −5% after inflation) is a made-up test, not a forecast or a piece of history. Try your own. Then try the “spend less” box to see how much a little flexibility buys back.

The 4% rule guide walks through the research and three tools people use: a bond tent, a cash buffer and spending guardrails.

Real return, default 5%. “Real” means after inflation. Working in real terms keeps every result in today's dollars, so a FIRE number 15 years away still means what it means today, and we don't need a separate inflation guess. 5% after inflation is a middle-of-the-road planning assumption for a portfolio that holds mostly stocks. It is not a forecast, and markets don't deliver a steady return. Try 3% or 4% to see a more cautious picture.

Safe withdrawal rate, default 4%. This is the “4% rule.” It comes from William Bengen's 1994 paper (opens in a new tab), which used historical U.S. stock and bond returns to test how much a retiree could take out in the first year, then raise each year with inflation, without running out. A later study, often called the Trinity study (1998) (opens in a new tab), tested withdrawal rates over payout periods of 15 to 30 years; Bengen tracked how long portfolios lasted out to 50 years, but framed his 4% around a minimum of 30. If you stop work at 40, your money may need to last 50 years or more, so it's worth testing a lower rate such as 3.5% or 3%.

This calculator uses one steady return, or one rough patch then a steady return. The research replayed real history, year by year, which is bumpier than either. Use this to see the shape of the risk, not to find a “safe” number.

Enter only the spending your savings have to cover. If a pension or Social Security will pay part of your costs later, the Pension + FIRE calculator maps the bridge years before it starts. If you'll earn a little, the Barista FIRE calculator shows how it shrinks what you need.