The 4% Rule: How Much You Really Need to Retire
"How much do I need to retire?" sounds like it should need a financial adviser and a spreadsheet the size of a wall. It doesn't. There's a shortcut that has guided the early-retirement movement for thirty years, and it fits in a single line: multiply what you spend in a year by 25. That's the 4% rule in reverse — and while it isn't gospel, understanding it will change how you think about your finish line.
Where the 4% rule came from
In the 1990s, financial adviser William Bengen tested every 30-year retirement window in modern US market history to find the highest withdrawal rate that never ran out of money. The answer was about 4% of the starting portfolio, rising with inflation each year. A later study by three professors at Trinity University reached a similar conclusion, and the name stuck. Investopedia has a clear write-up if you want the original sources; el estudio original de William Bengen (1994) is where it all began.
The 25x shortcut
Flip 4% around and you get a rule you can do in your head: whatever you need per year, multiply by 25. Spend €30,000 a year? You're aiming for roughly €750,000. Spend €50,000? Around €1.25 million. It works because withdrawing 4% is the same as needing 25 times your annual costs. Suddenly retirement stops being a fog and becomes a target you can actually plan toward.
What the rule gets right
Its real gift is reframing the question. Most people think retirement is about hitting a scary lump sum; the 4% rule shows it's really about your spending. Trim €500 a month from your future budget and you've just knocked €150,000 off the number you need. It also builds in a crucial assumption — that your money stays invested and keeps growing through retirement, which is why an all-weather portfolio matters more than a big cash pile. Our guide to a global ETF portfolio covers how that's usually built.
Where it falls short
The rule is a guide, not a guarantee. It was built on historical US returns, and the future may be stingier. It assumes a 30-year retirement — retire at 45 and your money has to last far longer, so many early retirees use 3.25–3.5% instead. And it ignores sequence risk: a brutal crash in your first few retired years does far more damage than the same crash later, because you're selling while prices are down. Treat 4% as a starting hypothesis, not a promise.
How to use it without betting your future
Smart retirees keep the rule but add guardrails. Hold a cash buffer of one to two years' spending so you're not forced to sell shares in a downturn. Stay flexible — trimming withdrawals slightly in bad years dramatically improves how long the money lasts. And keep a slice in growth assets even in retirement; the power of compounding doesn't switch off the day you stop working. The rule gives you the target; these habits protect it.
Run your own numbers
Averages are useful right up until they're about your life, so put your own figures in. Estimate your real annual spending, multiply by 25, and you've got your goal. Then work backwards: our compound interest calculator shows what monthly investment reaches that number by your target date, and the passive income calculator models the income your portfolio could throw off once you're there. Pair them and "someday" becomes a plan with a date on it.
Find Your Retirement Number
Use the free compound interest calculator to see what monthly investment gets you to 25x your spending.
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Passionate about finance and investing, with more than 6 years of hands-on experience in the crypto world. He shares analysis and financial education on his YouTube channel, Cripto Adicto.
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