The Most Important Number for Your Retirement Planning

Jeremy Keil explains why personalized longevity estimates are the most important number in your retirement planning.

When most people think about retirement planning, the first number that comes to mind is how much money they’ll need to retire. And while that’s an important figure, I believe there’s another number that matters even more. I call it your retirement longevity number – and understanding it could have a significant impact on your retirement.

Why Your Retirement Longevity Number Matters

Your retirement longevity number is about more than just life expectancy. It combines two crucial questions:

• When will your retirement begin?
• How long are you likely to live once it starts?

Those two factors together determine how long your retirement will actually last. And the truth is, most people get both wrong.

Many people assume they’ll work until 65. Yet surveys from the Employee Benefit Research Institute show that, on average, people retire about three years earlier than they expected. Health issues, job loss, or family responsibilities often force people into retirement before they’re ready.

On the other side of the equation, people underestimate their longevity. Too often, we use the wrong life expectancy number—like the one we see in news articles that cites the “average American life expectancy” of 78 years. But that’s the life expectancy of someone born today, not someone who’s already made it to 60 and beyond. If you’re reading this, you’ve already beaten those earlier odds.

Why the Newspaper Numbers Don’t Apply to You

Here’s the reality: if you’ve made it to age 60, your life expectancy isn’t 78. It’s closer to 84. And that’s just the average. Half of people will live longer than that.

But even more important is recognizing that life expectancy is not an expiration date. The chance you’ll die exactly at your life expectancy is only about 3.5%. That means almost everyone will live either shorter or longer than that estimate.

So if you’re planning to retire at 65 and think you’ll only need your money to last until 78, you’re setting yourself up for a rude surprise. In reality, the average person retiring at 62 will live until 84. That means planning for a 22-year retirement instead of the 13 years you might have originally expected. That’s a 69% longer retirement than you thought you’d need to prepare for.

The Cost of Underestimating Retirement

Getting your longevity number wrong can have big financial consequences. If you underestimate how long you’ll live, you risk running out of money when you need it most. If you overestimate, you may end up working longer than you have to, or living too conservatively in retirement.

That’s why it’s so important to get a personalized estimate. Don’t just pull a number out of the air—like 85, 90, or 95. Instead, use tools designed to give you a better estimate based on your unique situation.

A Better Way to Estimate Longevity

One resource I recommend is LongevityIllustrator.org. In just five minutes, you can input your age, health, and other personal factors to get a more realistic picture of how long you might live.

This isn’t about predicting the future with certainty. It’s about preparing yourself for a range of possible outcomes so you and your family aren’t caught off guard.

Once you have your number, start by asking:

• What happens if I live shorter than expected?
• What happens if I live longer than expected?

Building your retirement plan with these possibilities in mind gives you flexibility and security no matter what happens.

Start Three Years Earlier

Another simple adjustment I encourage people to make is to move up their retirement age estimate by three years. If you think you’ll retire at 65, run the numbers as if you’ll retire at 62. That way, you’ll be ready if retirement comes sooner than expected.

And here’s the good news: being financially ready earlier gives you more options. You might retire early by choice. Or, if circumstances push you out of the workforce, you’ll be prepared instead of panicked.

Why This Number Should Come Before Everything Else

In my book Retire Today, I outline five steps to creating a retirement master plan. But before even starting with step one, I encourage you to begin with what I call step zero—figuring out your retirement longevity