Social Security disability insurance (SSDI) is a federally operated and regulated disability insurance program. Workers pay for this federal insurance through Federal Insurance Contribution Acts taxes. The amount of the monthly SSDI benefit is based on a weighted formula that the Social Security Administration applies to calculate benefits for each approved applicant. SSDI operates to provide disability benefits to disabled individuals who are too young to receive Social Security old age (retirement) benefits. This chapter presents a table with unedited data on disabled worker beneficiaries paid from Social Security's Disability Insurance Trust Fund. Supplemental security income (SSI) is a federal program that pays monthly benefits to low-income aged, blind, and disabled individuals. The SSI definition of disability for adult applicants is the same as the test in the SSDI program. Only individuals having low incomes and limited financial assets are eligible for SSI.