Why would someone get two checks?

In certain circumstances, someone can get both SSI and SSDI. This happens when someone is approved for SSDI, but their monthly check is lower than the full SSI Federal Benefit Rate (FBR)*. This could be due to earning low wages throughout the employment history or limited recent work. In this case, the individual will receive SSI to supplement the payment to bring them up to the FBR. Since the Social Security Administration (SSA) discounts the first $20 of earned or unearned income an individual receives when calculating the SSI amount, a concurrent beneficiary will receive $20 above the SSI FBR.

*The Federal Benefit Rate changes annually and can be found at SSA Annual Updates.