The 4% Rule: How Much Money You Actually Need to Retire

"How much do I actually need to retire?" is one of the most-asked questions in personal finance, and it's also one of the few with a genuinely simple, back-of-napkin answer. It's called the 4% rule, and once you understand it, you can estimate your own retirement number in about thirty seconds.

The formula

Retirement Number = Annual Expenses × 25

That's the whole thing. Spend $50,000 a year? You'd need roughly $1,250,000 invested. Spend $80,000 a year? Roughly $2,000,000. The "×25" comes from the idea that withdrawing 4% of your portfolio each year is historically a level that a well-invested portfolio could sustain over a long retirement.

Where the number comes from

It's based on research (often called the Trinity Study) that tested historical US market returns against 30-year retirement periods, asking a specific question: what withdrawal rate, adjusted for inflation each year, would have survived every historical period tested without running out of money? Roughly 4% held up as a level that worked in the large majority of historical scenarios.

How the withdrawal actually works year to year

You withdraw 4% of your portfolio's value in year one. After that, you withdraw that same dollar amount, adjusted for inflation, regardless of what the market does — not 4% of whatever the new balance happens to be. A $1,000,000 portfolio supports $40,000 in year one; if inflation runs 3%, year two's withdrawal becomes $41,200.

Where the 4% rule gets shaky

The original research was built around a 30-year retirement window. If you're planning a traditional retirement in your 60s, that fits reasonably well. If you're aiming for an early retirement in your 30s or 40s, your money may need to last 50 years or more — a withdrawal rate that survives three decades doesn't automatically survive six. Many early-retirement planners use a more conservative 3% to 3.5% instead, which pushes the target number higher.

It also assumes a rigid budget

The classic version of the rule assumes you withdraw the same inflation-adjusted amount every single year, no matter what the market is doing. In practice, most retirees naturally spend a bit less during a market downturn and a bit more during strong years — that kind of flexibility tends to make a portfolio last meaningfully longer than the rigid version the original research tested.

A guideline, not a guarantee

The 4% rule is a genuinely useful starting point for estimating a retirement target — not a risk-free promise. It's based on historical US returns, and no withdrawal rate can guarantee identical results going forward. Use it to get a real, actionable number, then build in flexibility around it rather than treating it as an exact science.

Want to actually build a plan around this number?

Getting your target number is step one. Our free course walks through the rest — how savings rate affects your timeline, how to invest for the goal, and how to protect the plan once you get there.

→ Start the Financial Independence course, or go straight to the full lesson on the 4% Rule and Safe Withdrawal Rates for the deeper version of this math.