Kathy Salvadore walks into her house from her morning run. She’s fit…make that really fit. The retired PE teacher has been competing in triathlons since the early 1980s.

Kathy could start to collect her Social Security checks. She’s sixty-two. She has worked at least 40 quarters (ten years) so these factors make her eligible. But she’s refusing those checks…for now. Plenty of people don’t. They take Social Security payments as soon as they can.

That makes sense if they need the money. Their savings might be limited. They might not be collecting a defined benefit pension or an inheritance from Auntie Joan. But plenty of others don’t immediately need the money. If they’re healthy, and they collect Social Security early, they might be tossing money away. They can receive more income if they wait.

Jane Bryant Quinn detailed this in her recent book, How to Make Your Money Last. Her research comes from Social Security experts Laurence Kotlikoff, Bill Reichenstein, and Russell Settle. Kotlikoff is the founder of MaximizeMySocialSecurity.com. Reichenstein co-authored Social Security Strategies: How To Optimize Retirement Benefits. Russell Settle is the founder of SocialSecurityChoices.com.

Bryant Quinn’s premise of waiting to juice your bounty reminds me of Walter Mischel’s so-called “marshmallow test.” The researcher began his experiments at Stanford University’s Bing Nursery School in the 1960s. His research team offered children a treat of their choice. They could eat that treat right away. But if they had the willpower to wait 20 minutes, they could have two treats.

Bryant Quinn says more retirees would do likewise if they knew about the extra treats. “Millions of retirees are letting part of their Social Security pensions go to waste,” she says. “So many people don’t even know about their Social Security options or don’t investigate what those options are worth.”

But Kathy Salvadore isn’t one of them. The sixty-two-year-old is fitter than most women half her age. She can also live on her teachers’ pension. If she defers her Social Security payments until she’s sixty-six years old, she’ll get 33 percent more each month, plus a cost of living adjustment. If she suspends those payments until she’s seventy years old, Kathy’s Social Security payments will be 76 percent higher than if she had started to take the money when she turned sixty-two.

Plenty of retirees ask about a break-even point. They wonder how long they would have to live for the waiting to makes sense. Bryant Quinn says the break-even point is about seventy-eight years of age.

Let’s assume you had taken the money early and died before your 78th birthday. In such cases, you would have received more income than if you had deferred taking payments.

On the other hand, if you had deferred payments until you were seventy years of age, and you lived until you were seventy-nine, you would have earned more income than if you had started to take the money at age sixty-two.

But if you’re healthy in your sixties, don’t bet on an early death. As Bryant Quinn says, “If a married couple reaches 65, the chance that one of you will live until 90 is better than 40 percent.” Deferring Social Security might be even more important for those with a dependent spouse.

Plenty of women, for example, didn’t work while they were raising children. If they entered the workforce late, they might not have earned enough for their own Social Security accounts. Such dependents would receive Social Security payments based on a percentage of their spouses’ retirement benefits.

In this case, if the working spouse deferred payments, it would boost the lifetime income of the dependent spouse–even if the primary breadwinner kicked the bucket soon after taking benefits.

Bryant Quinn’s book describes much more. Retirees should read it. And if you’re looking for a detailed look at your own Social Security options, there are plenty of places to turn. The AARP’s Social Security Calculator is available for free online. For a more personal report, you could use the online service at SocialSecurityChoices.com. It costs $39.99. MaximizeMySocialSecurity.com charges $40. It costs $150 an hour for one-on-one advice.

Not everyone has the resources to wait for their Social Security checks. But for those that can, it’s much like the so-called “marshmallow test.” If you don’t eat the marshmallow today, you can have (almost) twice as much tomorrow.

Andrew Hallam is a Digital Nomad. He’s the author of the bestseller, Millionaire Teacher and Millionaire Expat: How To Build Wealth Living Overseas