A married person with a small Social Security record of their own, or none at all, can collect a benefit based on their spouse's work record. It's called the spousal benefit, and it can be as much as half of the spouse's full benefit. The full benefit means what the worker would get at full retirement age, which is 67 for anyone born in 1960 or later.
Social Security pays your own benefit first and then tops it up. Say one spouse's full benefit is $2,400 a month and the other's own record pays $800. Half of $2,400 is $1,200, so the lower earner gets their own $800 plus a $400 spousal top-up, for $1,200 at full retirement age. The higher earner's check doesn't actually shrink, because the top-up is paid by the program on top of the worker's benefit.
Claiming early shrinks both pieces, and the cut is permanent. Claim at 62 with a full retirement age of 67, and your own benefit drops 30%, so the $800 becomes $560. The spousal top-up drops 35%, so the $400 becomes $260. Together that's $820 a month instead of $1,200, for life, apart from the yearly cost-of-living raises. The early claimer does collect five extra years of checks, about $49,200, but the bigger check catches up at around age 78. Live past that, and waiting comes out ahead.
Waiting past 67 doesn't help the spousal part. Your own benefit grows 8% a year from full retirement age to 70, but the spousal top-up stops growing at full retirement age. For a lower earner whose check is mostly top-up, there's little to gain by waiting past 67. The higher earner is a different story: waiting to 70 raises their own check, and it raises the survivor benefit, which is the check the household keeps when one spouse dies.
The worker has to have filed for their own benefit before a spouse can collect on their record, which trips up a lot of couples. You also can't take the spousal benefit now and switch to your own later. Anyone born on or after January 2, 1954, is treated as filing for both at once and gets whichever amount is larger. Divorced spouses can collect too, if the marriage lasted at least ten years, you're unmarried now, and your ex is at least 62. If you've been divorced at least two years, your ex doesn't have to have filed yet. Either way, your benefit doesn't reduce your ex's.
If either of you plans to keep working while collecting before full retirement age, part of the check can be held back, which I covered in the Social Security earnings test. I'm a licensed insurance broker, not a Social Security specialist, and the numbers here are an example. Your own figures are on your statement at ssa.gov.
Each of you can log in to my Social Security at ssa.gov and write down your benefit at full retirement age. Take half of the larger number and subtract the smaller one. If the result is above zero, it's the most the spousal top-up can add each month.