What Is the 4% Rule? The Simple Math Behind Early Retirement

The 4% Rule says that if you withdraw 4% of your portfolio in your first year of retirement, then raise that amount with inflation each year, your money has historically lasted at least 30 years in most cases.

It is not a guarantee, but it is not a theory someone made up either — it comes from decades of real market data.

Where It Comes From

In 1994, financial planner William Bengen tested withdrawal rates against U.S. stock and bond returns going back to 1926. Four years later, three finance professors at Trinity University — Cooley, Hubbard, and Walz — ran a similar analysis. Their question was simple: what withdrawal rate lets a retiree get through a 30-year retirement, including crashes, recessions, and everything in between?

Nobody reads academic papers for fun — but this one got around fast, and the reason is pretty obvious.

For a mix of stocks and bonds, the answer came out around 4%.

The Math in Plain English

If you have $1,000,000 invested, 4% of that is $40,000. You can spend $40,000 in your first year, then adjust that amount for inflation each year. In most historical 30-year periods the money lasted, and often the portfolio even grew. But the rule does not promise to keep the original million intact: in the worst periods, the balance shrank a lot.

Flip it around: if you know how much you spend per year, multiply by 25. That is your FIRE number.

• Spend $30,000/year → need $750,000
• Spend $50,000/year → need $1,250,000
• Spend $80,000/year → need $2,000,000

A Worked Example

James is 38. He works in logistics, spends about $42,000 a year and invests about $2,500 a month. He has $89,000 saved. His FIRE number: $42,000 x 25 = $1,050,000. At a 5% real annual return, he is roughly 18 years away. If he raises his monthly investing by $1,250, that drops to about 14 years. He retires at 52 instead of 56.

What the 4% Rule Gets Right

It is based on the worst periods in market history — not average years. The original Trinity Study (1998) tested retirements using U.S. market data from the 1920s to 1995, including the Great Depression and the 1970s stagflation; a later update by the same authors extended the data through 2009. Simple enough to actually use. You do not need a financial advisor or a spreadsheet with 47 tabs.

What the 4% Rule Gets Wrong

It was designed for 30-year retirements. If you retire at 40 and live to 90, you are looking at a 50-year retirement. Many FIRE researchers now suggest 3.5% for longer timelines.

It does not adjust for your life. Kids, health issues, a major move — your expenses change. Recalculate every year.

It assumes you stay invested. If you panic-sell during a crash, the math breaks.

The Part Nobody Talks About

Many people who reach their FIRE number do not stop working completely. They shift — fewer hours, different work, things they actually want to do.

Many do not want to stop working at all — they want the freedom to choose.

Working without knowing what the finish line looks like is the default. Running the numbers often reveals two things at once: the target is further than assumed, and there was no particular direction before. Knowing the number changes how every financial decision after that gets weighed.

That is when someday stops being a dream and becomes a deadline you are actually looking forward to.

FAQ

Is the 4% Rule still valid in 2026? Mostly yes. Some researchers suggest 3.5% to 3.8% is more conservative. For most people doing rough planning, 4% remains a solid starting point.

Does the 4% Rule work in any country? It was built on US market data. If you are investing outside the US, a slightly lower rate adds safety.

What if I have a pension or Social Security? Subtract that income from your annual expenses first. Your portfolio only needs to cover the difference.

Can I use the 4% Rule with index funds? Yes — it was designed with a mix of stocks and bonds in mind.

Try It Yourself

Honestly, just plug in what you spend and see where you stand. That is it.

Use the FirePath Tools FIRE Number Calculator

Written by Sebastian Cole, a pen name. I build these calculators and publish the assumptions behind every number so you can check them yourself.

The 4% Rule was introduced by William Bengen (1994) and popularized by the Trinity Study (Cooley, Hubbard and Walz, 1998). It is a guideline, not a guarantee. Consult a financial advisor for personalized advice.