Americans can start receiving Social Security benefits between the ages 62 and 70. Recent proposals to raise the retirement age have raised fears about slashing income to seniors. But a new paper points out that for some seniors, joining Social Security later can actually boost their lifetime income, depending on their health, marital status and the country's interest rates.

(Bradly C. Bower/AP)

There is already a built-in incentive for delaying Social Security benefits: Those who wait to sign up are expected to collect benefits for less time, so the government adjusts their benefits upward according to an actuarial formula. It didn't always pay off to join later. But nowadays, the combination of longer life expectancy, new rules regarding couples and historically low interest rates allows some late joiners to collect more Social Security benefits over their lifetimes, according to a new paper for the National Bureau of Economic Research:

We have shown that for real interest rates close to zero, delaying receipt of Social Security is actuarially advantageous for a large fraction of households, even those with mortality rates that are twice the average. At real interest rates closer to their historical average, delay is not actuarially advantageous for single individuals with mortality that is substantially above average; however, for married couples, primary earners with above-average mortality can gain from delay by passing on a higher survivor benefit to their spouses.

In other words, for those who can afford to wait, delaying Social Security benefits can pay off, particularly for healthy individuals and married couples.

The potential advantage however, fluctuates wildly depending on the interest rate: For healthy single women, joining at age 70 boosts their net Social Security benefits by 24 percent over their lifetimes when interest rates are assumed to be zero, while that gain drops to 7 percent at best when interest rates are 2.9 percent, no matter how long they wait. The most that less healthy single men can expect to gain from delaying benefits is 1.5 percent over their lifetimes, if they wait until age 65, and there's no benefit from waiting when interest rates are closer to historical norms.