SSDI is a disability insurance program financed by your Social Security paycheck deductions. Unless prohibited by your age, you must have worked a total of 10 years (40 quarters), 5 of which must be within the last 10 years (20 of the last 40 quarters). In order to be eligible for SSDI benefits, you must have earned FICA-taxed wages during this work period. For Supplemental Security Income (SSI) benefits, no work time is required at all. There are, however, limits to eligibility based on how much property you own or money you have in the bank, as the SSI program is aimed at individuals who lack income or resources and are disabled. Benefits are paid as a flat rate, and the amount may be reduced if you receive any money or assistance from any source. With both SSI and SSDI, you must be found disabled. The Social Security Administration (SSA) oversees both programs and defines disability as being unable to perform any “substantial gainful activity.”