How Long Will My 401(k) Last in Retirement?

You spent decades filling up your 401(k). Now the question that keeps you up at night flips around: instead of “how much can I save?” it’s “how long will my 401(k) actually last — and what happens if I run out?” It’s the right question to ask, and the honest answer is it depends— but not in a hand-wavy way. How long your 401(k) lasts comes down to a handful of numbers you can actually estimate. This guide walks through the math, the rules of thumb, the 401(k)-specific traps, and how to find your real number instead of a generic one.

The short answer

How long your 401(k) lasts depends mostly on three things: how much you withdraw each year, what your investments earn, and how long you live. As a rough benchmark, a balanced 401(k) you withdraw 4% from each year is designed to last about 30 years. Spend faster, and the timeline shrinks quickly.

That 30-year figure is a starting point, not a promise. The rest of this article shows what moves the number up or down — and why the single answer most calculators give you is more fragile than it looks.

The simple math (and why it’s only a starting point)

At its most basic, how long your money lasts is your balance divided by what you pull out, adjusted for growth along the way. Here’s roughly how a $500,000 401(k) behaves at a 5% average annual return, before counting Social Security:

The pattern is the real lesson: small changes in your withdrawal rate cause big swings in how long your 401(k) lasts. The problem is that this table assumes a smooth, steady 5% every year — and real markets never do that.

The 4% rule, applied to your 401(k)

The most common guideline is the 4% rule: withdraw 4% of your balance in your first year of retirement, then adjust that dollar amount for inflation each year after. On a $500,000 401(k), that’s $20,000 the first year; on $1 million, it’s $40,000.

The rule was built to survive a 30-year retirement even through rough markets. But it rests on assumptions — a roughly balanced stock/bond mix and average market history — that may or may not match your situation. The rule’s own creator, William Bengen, has since said the safe figure may be as high as 4.7%, while Morningstar’s 2025 research pegged a more cautious 3.9% as the safe starting rate. The takeaway: 4% is a reasonable anchor, not a guarantee.

Why the straight-line number can lie to you

Here’s what most “how long will my 401(k) last” calculators won’t tell you: the order of your investment returns matters as much as the average.Two retirees can earn the exact same average return over 25 years and end up in completely different places — if one of them hits a bad market in their first few years while withdrawing money.

This is called sequence of returns risk, and it’s the single biggest reason a confident single-number answer can be dangerous. When the market drops early in retirement and you’re still withdrawing, you’re forced to sell more shares at low prices — damage your portfolio may never fully recover from. A simple calculator that assumes a flat 6% every year hides this risk entirely.

The honest way to answer “how long will my 401(k) last” is to test it against manypossible market paths — including the bad-luck ones — and see your probability of success, not a single tidy number. Run your 401(k) through a free stress test to see how it holds up across 1,000 market scenarios, not just the rosy one.

401(k)-specific factors that change the timeline

Your 401(k) isn’t a plain savings account, and three quirks affect how long it really lasts:

• Required Minimum Distributions (RMDs). Starting at age 73(rising to 75 in 2033 under the SECURE 2.0 Act), the IRS forces you to withdraw a minimum amount from a traditional 401(k) each year, whether you need it or not. That can speed up withdrawals — and the tax bill.
• Taxes.A traditional 401(k) is pre-tax, so every dollar you withdraw is taxable income. A $40,000 withdrawal might leave you only ~$32,000–$35,000 to spend. A Roth 401(k) flips this — contributions were taxed, so qualified withdrawals are tax-free and have no RMDs for the original owner.
• Fees. Plan and fund fees quietly shave returns. A 1% difference in fees can cost years of portfolio longevity over a long retirement.

Social Security changes everything

Most people forget to subtract their other income. If you need $50,000 a year and Social Security covers $25,000 of it, your 401(k) only has to produce the other $25,000 — which can roughly double how long it lasts. The age you claim Social Security (62 to 70) dramatically changes this math, since delaying boosts your monthly benefit. Before you panic about your balance, map your full income picture, not just the 401(k) in isolation.

How to make your 401(k) last longer

You have more levers than you think:

1. Spend flexibly. Trimming withdrawals in down years is the most powerful protection against running out.
2. Delay Social Securityif you can — every year you wait (up to 70) raises your guaranteed income.
3. Mind the withdrawal order— drawing from taxable, then tax-deferred, then Roth accounts can stretch the total.
4. Keep a cash cushionso you’re not forced to sell investments during a downturn.
5. Revisit the plan yearly.Retirement income isn’t “set and forget.”

How to find your real number

A rule of thumb is a fine place to start, but your retirement is specific: your balance, your spending, your Social Security, your timeline. Instead of guessing, test how long your 401(k) will last free — no sign-up. The calculator models inflation, Social Security, and a thousand market scenarios (including bad early years) so you see a realistic probability your money lasts, not a single fragile figure. For the bigger picture, see how long your total savings will last in retirement.

Frequently asked questions

This article is for educational purposes only and is not financial advice. Everyone’s situation is different. See our full disclaimer.

Sources: William Bengen (1994); Morningstar, “The State of Retirement Income” (2025); U.S. Internal Revenue Service (RMD rules under the SECURE 2.0 Act of 2022); Social Security Administration. See our methodology.