Dear Liz: My spouse’s parents were married for 11 years. They divorced at age 32 and my mother-in-law remarried at 42. My mother-in-law and her ex are now 82. Her husband is 93 and in poor health. When her husband dies, she does not get his pension. Her current Social Security benefit is $850 a month. Her husband receives $1,200 while my father-in-law’s benefit is $2,500 a month. She is convinced that when her current husband dies, she will be eligible for her ex-husband’s $2,500 benefit. I think that only happens when her ex dies, but she can get 50% while he is still alive. What is correct?

Answer: You’ve got it right.

People may be eligible for benefits from ex-spouses’ work records if the marriage lasted at least 10 years.

While the ex is alive, your mother-in-law could qualify for divorced spousal benefits of up to 50% of his benefit at full retirement age — but only if she is currently unmarried. If her ex dies, she might be eligible for divorced survivor benefits of up to 100% of the benefit he was receiving — but only if she is widowed or divorced. (People can receive divorced survivor benefits while married, but only if they married at 60 or later.)

She would receive benefits based on her ex’s work record only if the check is larger than her own.

The different rules for divorced spousal versus divorced survivor benefits can be complicated, so it’s not surprising that she’s confused. Let’s use the numbers you provided to make this somewhat clearer.

If she is widowed and her ex is still alive, she would get a divorced survivor benefit of $1,250, because it’s (slightly) larger than the $1,200 survivor benefit from her husband’s record. (Her own $850 benefit would essentially go away, so her household income would drop pretty dramatically from $2,050 plus the pension to $1,250.)

If her ex should subsequently die, she would be eligible for divorced survivor benefits of $2,500 (or whatever the ex was receiving at the time of his death).

There are some caveats here.

Divorced spousal benefits are based on the ex’s “primary insurance amount,” or what he would receive at his full retirement age. For someone born in 1940, that was 65 years and six months. Your mother-in-law would not be eligible for any delayed retirement credits her ex may have earned by putting off his application until after his full retirement age.

On the other hand, she wouldn’t be penalized if he started his benefit before full retirement age. The bottom line is that her divorced spousal benefit could be somewhat more or less than 50% of what he is currently receiving, depending on when he applied.

Survivor and divorced survivor benefits, on the other hand, are based on what someone was actually getting when they died. An early start can stunt those benefits whereas a later start can increase them.

That’s true of regular survivor benefits as well, and why it is so important for the higher earner in a married couple to delay filing as long as possible. The larger benefit can really help when the first spouse dies and one of the couple’s two checks ends.

Your mother-in-law’s financial prospects were made even worse by the decision to get a “single life” payout from the pension rather than a “joint and survivor” option. The joint and survivor option would have meant accepting a smaller benefit, but it would have lasted for your mother-in-law’s lifetime rather than ending at her husband’s death.

A married worker can’t choose the single life option without spousal consent, and spouses would be smart to consult a fee-only financial planner before they agree to give up a lifetime stream of income.