Social Security Disability, or SSD, and Supplemental Security Income, SSI, are similar, yet different. Both are forms of income that you may be entitled to if you become unable to work.
However, Social Security Disability is paid based on your earnings history. The amount does not change from month to month.
Supplemental Security Income, SSI, is paid on a sliding scale based on your resources and need. This is for individuals who may not have an earnings history, children, or people who have been out of the workforce for a long time.