A legal separation does not affect a person's rights to any Social Security benefits he's earned, and only divorce will prevent him from drawing spouse benefits. For the Supplemental Security Income program, physical separation, and not legal separation, will affect the benefit amount.
Spouse Benefits in Social Security
The Social Security program allows workers to claim retirement or disability benefits on the basis of their lifetime earnings. For a married couple, the program also offers spouse benefits to an individual who has not accrued enough credits to claim personal Social Security. These benefits max out at 50 percent of the earner's benefits. For example, if a husband has worked enough to draw $1,000 in monthly benefits, his wife is entitled to $500 a month.
Social Security considers someone a spouse if he is legally married. Even if there is a legal separation or separation agreement in effect, he's still married for Social Security purposes. That means full spouse benefits are also available, but there is a catch. The spouse can only apply for them after the principle earner files the application for his own benefits. It is possible for the principle earner to claim and then suspend benefits. That allows the spouse to draw the spouse benefits even if the principle earner delays the payments.
Marital status, legal separation and divorce don't enter into the calculation of Social Security disability benefits. That program allows disabled applicants to draw regular benefits, even before they reach retirement age, if the disability prevents them from earning a minimal income. The amount they get is based on their own record of earnings. Disability applicants qualify individually on the basis of their medical condition. They must show proof of that through medical records and doctor opinions.
SSI and Separation
Social Security also administers the Supplemental Security Income program for disabled individuals who don't have enough Social Security credits to draw disability benefits. The SSI program rules limit the income and assets of qualifying applicants. For a married applicant, the income brought in by the spouse is "deemed," or considered available, if the couple is living together. There is no deeming if the spouses live apart. Social Security pays single SSI beneficiaries at 100 percent of the federal benefit rate ($733 monthly in 2015). Qualified married couples living together draw only 75 percent of that rate. SSI will pay both 100 percent of the rate if they are physically separated.