SSDI benefits are entitlement programs employers, workers, and the self-employed pay for with the Social Security tax levied on their earnings. Benefit eligibility is based on an applicant’s work history (or a parent or spouse’s), while earnings determine the benefit amount. SSI is a needs-based program for individuals with limited resources (assets or things they own) and income. General tax revenues fund this program, and federal and state laws determine the benefit amount. The benefit amount an applicant receives considers their income, where they live, and who lives with them.