The 4% Rule: How to Turn Your Annual Expenses Into a Target Number

One question comes up very early in any serious conversation about financial independence: how much is actually enough? Not “comfortable” or “more than enough” — enough. The specific number at which you can stop working and not run out of money.

For most people pursuing FI, the answer starts with the 4% Rule.

What the 4% Rule Says

The 4% Rule is a withdrawal guideline: in your first year of retirement, you can withdraw 4% of your invested portfolio, then adjust that amount upward for inflation each year, and have a very high probability of your money lasting at least 30 years.

In practice, most people use it the other way around — not to calculate what to withdraw, but to calculate what they need to accumulate. The math is straightforward:

Annual Expenses × 25 = Your FI Number

The 25 comes from flipping 4% upside down (100 ÷ 4 = 25). If your household spends $52,000 a year, your FI number is $1,300,000. That’s the portfolio size at which, historically, you could stop working and expect your money to last.

Where This Rule Came From

The 4% figure wasn’t invented casually. Financial advisor William Bengen published it in 1994 after back-testing withdrawal rates against US market data going back to 1926. He wanted to find the highest withdrawal rate that would have survived every 30-year period in modern history — including the Great Depression and the stagflation of the 1970s.

The conclusion was later reinforced by the Trinity Study (1998), a widely cited paper from Trinity University that ran similar simulations across different portfolio allocations. Both arrived at roughly the same answer: 4% holds up across a remarkable range of historical conditions.

What It Assumes — and Where It Has Limits

The 4% Rule is a useful starting point, not a guarantee. It was designed around a 30-year retirement horizon and a portfolio split between US stocks and bonds. If you plan to retire significantly earlier — say at 40, meaning a 50-year horizon — a more conservative withdrawal rate of 3.5% or 3% is worth considering. That means a multiplier closer to 28 or 33 rather than 25.

It also doesn’t account for flexibility. Most people who reach FI aren’t rigidly withdrawing a fixed percentage regardless of market conditions. In a bad year, they spend a bit less or earn a little income from occasional work. That flexibility makes the real-world risk considerably lower than any static model suggests.

Why It’s Still the Right Starting Point

Despite its limitations, the 4% Rule does something no vaguer framework can: it gives you a concrete number to aim for. “I want to be financially independent” is aspirational. “I need $1.1 million invested” is a target you can measure your progress against every month.

That concreteness is why it remains the foundation of most FI planning. The independence.money calculator uses it to convert your current expenses into your personal FI number. Once you see that figure, the question shifts from “is this even possible?” to “how long will it take?” — which is a much more tractable problem.