You've probably heard people say you're better off waiting to claim Social Security until your full retirement age (FRA) -- which is either 66 or 67 depending on your birth year -- or even waiting until age 70, when you qualify for the maximum benefit, but this isn't always true. There are certain situations when delaying Social Security to increase your checks would actually place an unnecessary strain on your finances, and it could even reduce the total benefits you receive during your lifetime.

Here are three instances when you should consider signing up for Social Security before you hit your FRA.

1. You aren't going to live long.

If you've been diagnosed with a terminal illness, there's no sense in delaying Social Security. If you wait until your FRA or age 70, you'll get more money per check, but ultimately dying before the benefit amount breaks even means less money overall if you didn't live long enough to collect those checks.

Social Security card with $100 bill

Image source: Getty Images.

Imagine this scenario: You're entitled to a $1,000 monthly benefit at your FRA of 67 and a $700 benefit if you start claiming at 62. If you expect to live until age 70, it's sensible to start claiming at 62. You'd receive $67,200 in Social Security benefits in your lifetime, compared with the $36,000 you'd get if you waited until your FRA to claim.

If you're relatively healthy now, you can look at your family history combined with your lifestyle to get a sense of how long you will probably live. For context, the current average life expectancy in the United States is 78.6 years, but this may be too low of an estimate for many. One in four 65-year-olds today can expect to live past 90, according to the Social Security Administration (SSA), and one in 10 can expect to live past 95.

2. You're unable to work and you need the income.

It's not an ideal situation, but if you've lost your job and you cannot find another one or you've become unable to work, starting Social Security early may be a smarter play than waiting. This guaranteed monthly income will ease the strain on your retirement savings and help stretch your nest egg further. Plus, you'll be able to leave more money invested in your retirement accounts where it can enjoy compounding growth for a few years longer, thanks to Social Security covering a portion of your living expenses.

Of course, Social Security alone may not be enough to cover all your expenses. Avoid drawing upon your retirement savings early by finding creative ways to make ends meet, like cutting your expenses, working part-time or starting a side hustle, or renting out a spare room on Airbnb for additional income.

3. You're married and you earn less than your spouse.

A common strategy used by married couples to maximize their Social Security benefits is for the lower earner to begin claiming benefits at as soon as possible at age 62 while the higher earner delays taking benefits until 70, when they're entitled to the largest possible check.

The lower earner's Social Security check will help the couple get by, covering some of their living expenses so they don't have to withdraw too much from their personal savings. Then, when the higher earner reaches age 70, they will be eligible for a larger check that will cover even more of the couple's expenses, further reducing the strain on their nest egg. Once the higher earner applies for Social Security, the lower earner may switch to a spousal Social Security benefit instead, if it offers a larger amount than what they're entitled to based on their own work record.

If you and your spouse make a similar amount of money, you could also use this strategy, but the difference in the total Social Security benefits may not be significantly different than what you'd get if you both waited until your FRA to claim. In that case, it may be better for both partners to delay Social Security as long as possible before claiming benefits.

If you anticipate a long life, it's probably better to delay Social Security as long as you can. But there are situations where it pays to start Social Security a little early, even if it means sacrificing the larger checks you could be entitled to later. So do the math to make sure you start drawing your benefits at the optimal time for you and your family.