If your mom waits until her own full retirement age to claim spousal benefits, she can benefit from another technique. If her spousal benefit is larger than her own benefit, she can get spousal checks for the years between her full retirement age and age 70. Then, once her own benefit has hit its maximum amount, she can switch from spousal benefits to a benefit based on her own record if that amount is greater.

If there's a dependent child in the mix, the rules change a bit. Your mom can receive a full spousal benefit -- up to half of her husband's full retirement benefit -- at any age, as long as her husband has filed for Social Security and the child is receiving benefits. (The children of Social Security recipients qualify for checks as well, as long as they're unmarried and under 18, or under 20 and full-time students, or disabled with a disability that started when they were younger than 22.) Your mom can receive her spousal benefit until the child reaches age 16. At that point, the child's benefits would continue but your mom's would stop unless she's old enough to receive retirement benefits (age 62 or older) or survivors' benefits as a widow or widower (age 60).

Your mom is divorced. Your mom can claim benefits based on her ex's record as long as:

  • She's at least 62.
  • The marriage lasted at least 10 years.
  • She's currently unmarried.

What's more, her ex doesn't have to cooperate. As long as he's 62 or older, he needn't have filed to receive his own benefits for her to claim a spousal check, and his approval isn't needed. It will help the application process if your mom has his Social Security number, but the Social Security Administration says it can track down his records without it.

The benefit amount and rules for collecting are the same for a divorced spouse as for a current spouse. As noted above, claiming a spousal benefit doesn't reduce the ex's benefits, or affect the benefits of his current spouse or any other former spouses. But as with other retirement benefits, choosing to take the money early will result in a permanent reduction in your mom's checks. If she continues to work, the check could be reduced further by the earnings test.

If she delays claiming her spousal benefit until she reaches her own full retirement age, she'll also preserve the choice to switch to her own retirement benefit at age 70, if that amount is greater.

What if your mom remarried after her divorce? She can't claim benefits based on an ex's record if she's still married to a subsequent spouse. But if the later marriage ends -- by divorce, annulment or death -- she can apply for benefits based on either previous spouse's record.

Your mom is widowed or her ex has died. Once a breadwinner dies, so does the 50% limit on spousal benefits. Your mom can claim up to 100% of the retirement benefit of a deceased spouse -- or a deceased ex. Furthermore, she can receive benefits at a younger age -- 60, or 50 if she's disabled -- and she can even remarry, as long as she does so after age 60.

To qualify for a survivor's benefit, she typically must have been married to the covered worker for at least nine months before his death. If they were divorced, the marriage must have lasted at least 10 years.

The nine-month minimum for current spouses has some exceptions. If the breadwinner died in an accident or in the line of duty as a member of a uniformed service, or if the couple was previously married to each other and the past marriage lasted nine months, the minimum is waived, and the survivor can apply for benefits.

As with other Social Security benefits, claiming a survivor's benefit before she reaches full retirement age will result in a smaller check, but the minimum is typically 71-1/2% of the dead spouse's benefit. If the person who died was receiving reduced benefits, the survivor's check is based on that reduced amount.

Another difference between spousal and survivor benefits is more flexibility in switching between benefits. If your mom receives benefits as a surviving spouse or surviving divorced spouse, she can switch to her own retirement benefit as early as age 62. Or she can wait to switch until full retirement age to her own, unreduced benefit.

If your mother does remarry after 60, she may qualify for benefits both as a widow and as a spouse. She can choose which benefit to take, but she can't take them both. Social Security will calculate both benefits, and she can choose the larger one.

Clearly, Social Security has a lot of moving parts. It's easy to get confused and make a mistake that could result in a smaller benefit than what she's entitled to. What's important is educating yourself and running the numbers, using the Social Security benefits estimator and tools like AARP's retirement calculator, to understand all your options.

"At least then people won't do stuff because they didn't know any better," Peterson said.

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If you suspect your mom should be getting a bigger check, you or she can contact the Social Security Administration at 800-772-1213 to get the review process started.

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.