SSI, or Supplemental Security Income, is a program that pays benefits to adults and children who are disabled and have limited income. SSDI, or Social Security Disability Insurance, is an insurance payment paid to disabled individuals who qualify because their previous work wages were covered under the SSDI program.
Physical and mental impairments that prevent an individual for performing a substantially gainful activity qualify adults 18 and over for SSI benefits. These disabilities must be expected to last at least 12 continuous months, or result in the individual's death. Children under the age of 18 must have disabilities the limit their function, are long-term, or are expected to result in death. Eligible persons must be either resident aliens or U.S. citizens who do not leave the country for over 30 consecutive days.
SSDI pays monthly benefits to individuals who become disabled before they reach the age of retirement. To qualify for SSDI, the worker must have worked enough years to earn the necessary credits, and workers earn about four credits per year. The number of credits needed depends on the worker's age. The worker must also have a condition that meets the Social Security Administration's definition of a disability, and the condition must be severe and long-term.