The Social Security Administration recognizes that couples invest a lot into a long-term marriage. If you support each other through years of employment, you can collect on the benefits of your spouse under some circumstances. if your spouse elects to collect on your earnings rather than her own, however, there are plenty of rules and requirements.
Effect on Your Benefits
Even if you have multiple ex-wives, and if each of them collects based on your earnings, it won't affect your own benefits. You'll collect just as much as you would have if you had never married at all. It doesn't even matter if you haven't yet begun to collect your own benefits as long as you're eligible to do so. Your ex can collect on your earnings as long as she meets all other requirements and you've been divorced for at least two years.
Duration of Marriage
The greatest stumbling block to your ex-wife collecting Social Security based on your earnings is that your marriage must have lasted a while – at least 10 years. After you hit the 10-year mark, if you divorce the next day, your ex is entitled to collect, but if your divorce is final nine years and 11 months after the date of your wedding, she can't. There's no graduated scale where she can collect less if your marriage doesn't reach this benchmark. Because her collecting doesn't affect your benefits, the length of your marriage won't affect you at all.
Effect of Remarriage
Another potential pitfall – at least where your ex is concerned – is that she can't remarry. If she does, she can no longer collect on your benefits, unless she remarries you. However, if her second husband dies or they're divorced, she can resume collecting on your earnings after that occurs. If you remarry, the fact that your ex-wife is collecting has no effect on your new spouse's ability to do so as well, assuming you're married for 10 years or longer -- nor will your new spouse collect less than your first wife.
Social Security won't allow your wife to begin collecting until you've both reached the age of 62. You must be eligible to collect, and she must be eligible also. An exception exists for Social Security survivor's benefits, which are different from SSI. If you die, your ex can begin collecting survivor's benefits at age 60, or at age 50 if she's disabled. In some cases she can collect when she's even younger if you share a minor child for whom she's caring. There's no remarriage penalty if you die and your ex collects survivor benefits, as long as she doesn't marry until after she reaches age 60.
There are a few other catches to your ex-wife collecting on your earnings. Your benefits must be greater than hers, based on her own work history. If she's able to collect on her own work history, but her benefits are less than yours, Social Security will make up the difference so she receives as much as you do.