How Much Money Do You Actually Need to Retire?

Asking how much you need to retire sounds like a deeply personal question. The details are personal, but the math is simple. You can summarize it in one phrase: 25 times your spending. Here's where that comes from and how to use it.

The 4% rule, briefly

In the 1990s, a financial planner named William Bengen put a question to a century of market data. He wanted to know how much someone could withdraw from a diversified portfolio each year, adjusted for inflation, without running out of money over a 30-year retirement, even if they retired at the worst possible time. The answer came out to about 4%.

Flip that 4% upside down and you get the planning rule of thumb: a portfolio of 25 times your annual spending.

Annual spending in retirement	Portfolio target (25x)
$40,000	$1,000,000
$60,000	$1,500,000
$80,000	$2,000,000
$100,000	$2,500,000

Bengen's finding has been stress-tested plenty since, most famously by the Trinity Study, in which three Trinity University finance professors reran the withdrawal math across decades of market history and landed in the same neighborhood. This is the same rule that powers the FIRE movement, the community built around retiring as early as possible. The 25x math is their favorite tool for a reason. It turns "someday" into a number.

Spending, not income, is the input

The detail that trips people up: the input to this rule is your spending, not your income. A household earning $150,000 but spending $60,000 needs $1.5 million, not $3.75 million. Income determines how fast you can get there. Spending determines where "there" is.

Your retirement spending also won't match your working-years spending. Some costs disappear when you stop working: the commute, possibly a second car, the retirement contributions themselves, and the mortgage if you've paid it off. Other costs rise, especially healthcare and the activities you finally have time for. A common starting estimate is 70-80% of pre-retirement spending, but it's worth building your own number from your actual expenses, because your circumstances will move it more than any rule of thumb.

Finally, subtract Social Security. Your benefit will cover a meaningful chunk of spending for most people, so the portfolio only needs to cover the gap. Estimate your benefit, subtract it from your annual spending, and multiply what's left by 25. You can estimate your benefits here.

What the rule gets wrong

The rule is a good approximation, not the whole story. The 4% figure assumes a 30-year retirement, so if you're retiring early enough to need 40-50 years, plan around 3.25-3.5% instead, which works out to 28-30x your spending. Our FIRE calculator shows how the withdrawal rate changes your number. The rule also assumes a diversified stock and bond portfolio, so money parked in cash will not support anything close to 4%. It ignores taxes entirely, and those depend on your account mix: Roth withdrawals come out tax-free, while traditional 401(k)s and IRAs are taxed on the way out, so a dollar in each is not worth the same amount. And the rule is rigid where humans are flexible. Real retirees spend less in down markets and more in good ones, and that flexibility alone meaningfully improves the odds.

Researchers have rerun Bengen's math many times since, and depending on assumptions, the safe rate lands anywhere from about 3.3% to 4.5%. The 25x target holds up well as the planning anchor.

How to make it useful today

Start with an estimate of your annual spending in retirement, subtract expected Social Security, and multiply by 25. That's your rough number. Then use the retirement calculator to see what monthly contribution gets you there from your current age and balance.

The target will look ludicrous at first, because it is a genuinely large number. But it's an end goal, not this year's assignment, and the majority of the work gets done by compounding rather than by your contributions. The money you invest early does the heaviest lifting, and the balance grows faster every year it's left alone. See where you stand against the typical path in retirement savings by age.

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This article is for general educational purposes only and does not constitute personal financial, investment, tax, or legal advice. Consult a qualified financial professional before making major financial decisions. See our Disclaimer.