If your spouse has passed away, you may be entitled to Social Security survivor benefits. These can be a crucial income source once you no longer have a partner to help you make ends meet. 

Unfortunately, not everyone is aware of the rules surrounding spousal benefits -- and a lack of knowledge could cost you. To make sure you don't leave money on the table, it's important to know three key rules. 

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1. You can claim survivor benefits after a divorce if you were married for at least 10 years

Social Security survivor benefits are available based on your spouse's work history. But you do not actually have to be married at the time when you claim them.

If you have divorced after a marriage that lasted 10 or more years, it is possible to get survivor benefits. This is true even if you have remarried someone else, as long as you did not get remarried before age 60 (or before age 50 if you are disabled).

If you don't know that you can get survivor benefits even after a divorce, you could end up leaving money on the table that you are entitled to. You can't assume the Social Security Administration is going to inform you of all the benefits you are eligible for: An Inspector General report estimated thousands of seniors were missing out on survivor benefits they should have been receiving. This oversight cost them millions of dollars. 

2. You can claim them at a younger age than retirement benefits in many cases

If you are claiming Social Security retirement benefits, you can start them as early as age 62. But survivor benefits could become available at a younger age. You can get them at age 60 (or at age 50 if you are disabled).

While an early claim will shrink them, it's still beneficial to be able to begin getting payments sooner. You also have the option to claim your survivor benefits and then switch over to your own retirement checks later on if it would make sense to do so because your own benefit would be higher.

3. They could be reduced if the higher earner makes an early benefits claim

Finally, there's another important rule to know about survivor benefits. When both spouses are getting Social Security checks and one spouse dies, the last surviving spouse gets to keep the higher of the two payments that were previously coming into the household.

But if the person in the relationship who would have had the highest Social Security benefit claimed their checks early and reduced their check amount, this would result in a reduction in survivor benefits available. Many people don't realize this when they make an early Social Security claim, and as a result they end up leaving their partner in a difficult financial situation as a widow(er). 

By understanding all of the rules associated with survivor benefits, both people in a relationship can work together to make the best Social Security claiming choices -- and couples can make sure they collectively maximize their lifetime retirement income.