How Long Will My Money Last in Retirement? 5 Factors That Decide the Answer

Ask ten retirees how long their money will last and you'll get ten confident answers, most of them based on a rule of thumb they heard years ago. The truth is that the answer isn't one number. It comes from a handful of moving parts, and a small shift in any of them can change the result by years.

The good news is that there are really only five factors that do most of the work. Once you understand them, you can plug your own numbers into a calculator and make sense of what comes back. Let's go through them one at a time.

1. Your Withdrawal Rate

This is the big one. Your withdrawal rate is the amount you take out in a year, as a percentage of what you have saved. If you retire with $1,000,000 and spend $50,000 in the first year, your withdrawal rate is 5%.

You've probably heard of the 4% rule, which says that withdrawing 4% in the first year, then adjusting for inflation, has historically held up over about 30 years. It's a useful starting point, not a guarantee. What matters more is seeing how sensitive the outcome is. Here's what happens with a $1,000,000 balance, a steady 5% annual return, and the same dollar amount withdrawn every year:

Notice where the cliff is. Once you take out more than your portfolio earns, the balance starts to shrink, and every dollar withdrawn also stops earning anything for you. Going from 5% to 6% costs you the "forever" result. Going from 6% to 8% cuts the timeline nearly in half.

Keep in mind this table assumes a smooth 5% return every year and no inflation adjustments, which is a best-case setup. We'll look at why that rarely happens in the next two sections.

2. Investment Returns, and When You Get Them

Most calculators ask for an average annual return. That's reasonable, but averages hide something important: the order in which returns arrive matters when you're taking money out.

Picture two retirees who each start with $500,000 and withdraw $40,000 at the start of every year. Over four years, their investments earn the same four returns: +20%, +10%, -10%, and -20%. The only difference is the order. Retiree A gets the good years first. Retiree B gets the bad years first.

After four years, Retiree A has about $344,700 left. Retiree B has about $288,900. Same average return, same withdrawals, and a gap of more than $55,000. This is called sequence of returns risk, and it's the reason a market drop in your first few years of retirement is more dangerous than one that arrives later.

You can't control the market, but you can plan for it. Running a few different return assumptions, like a cautious 3%, a middle 5%, and an optimistic 7%, gives you a range instead of a single answer you might be overconfident about.

3. Inflation

Inflation is the slow leak that most people underestimate. At 3% a year, prices roughly double every 24 years. If you spend $4,000 a month today, you'd need about $7,200 a month in 20 years, and about $9,700 a month in 30 years, just to buy the same things.

Put another way, a dollar today buys what only about 55 cents will buy in two decades. Your savings need to cover not just the retirement you'd have today, but the one you'll have after prices keep climbing.

This is why it matters whether your plan uses flat withdrawals or inflation-adjusted ones. If you plan to raise your spending each year to keep up, your calculator needs to do the same. Otherwise it will tell you your money lasts longer than it really will.

4. How Long You Actually Live

The question "how long will my money last" only makes sense next to another one: how long does it need to last? Nobody knows, and guessing low is the more dangerous mistake. Commonly cited Social Security figures suggest that about one in four 65-year-olds today will live past 90, and roughly one in ten will pass 95. For a couple, the odds that at least one person reaches those ages are higher still.

So rather than planning to age 85 because that feels like an average life, many people plan to 95. If you retire at 65, that's a 30-year runway. Retire at 60 and you may need money to stretch for 35 years or more. A longer horizon means you either need a bigger balance or a lower withdrawal rate. There's no way around that trade.

5. Taxes and Healthcare Costs

Two expenses quietly reshape the picture: taxes and healthcare.

Withdrawals from a traditional 401(k) or IRA are taxed as ordinary income. If you want $60,000 to spend and your effective tax rate on withdrawals is about 15%, you'll need to withdraw roughly $70,600 to end up with $60,000 after tax. That bigger withdrawal comes out of the same pot, so it shortens how long the pot lasts. Roth accounts and taxable accounts behave differently, which is why many retirees draw from a mix.

Healthcare is the other wildcard. Medicare covers a lot, but premiums, deductibles, prescriptions, dental, vision, and any long-term care needs add up, and they tend to rise with age. Whatever number you budget for medical costs, it's worth leaving some cushion.

Putting the Five Factors Together

Here's a simple way to use all this. Take your balance, your planned annual spending, and your best guess at tax. Then run at least three scenarios in an investment calculator with withdrawals: one cautious, one realistic, and one optimistic, with inflation turned on. If your money lasts to age 95 in the cautious case, you're in strong shape. If it only works in the optimistic case, you have time to adjust.

And if the numbers come back tighter than you'd like, remember that you have levers: spend a bit less, work a year or two longer, delay Social Security, or stay flexible during down markets by trimming withdrawals until things recover. Small, early adjustments are far easier than big ones later.

Try It With Your Own Numbers

General examples only go so far. The most useful thing you can do is test your own situation. Use the how long will my money last calculator on this site to see how long your savings could last under different withdrawal amounts and returns. It takes about a minute, and it turns a vague worry into something you can plan around.

This article is for educational purposes only and is not financial, tax, or investment advice. Projections are estimates based on assumptions, and actual results will vary. Consider talking with a qualified financial professional about your specific situation.