SSI and SSDI are two different programs with some significant differences between them, but they are both administered by the Social Security Administration (SSA) and the definition of medical disability is the same for both programs.
SSDI, or Social Security Disability Insurance (otherwise known as SSD, Social Security Disability, or DIB, Disability Insurance Benefits) falls under Title 2 of the Social Security Act. SSDI provides disability benefits to individuals who have earned enough work credits for qualify. (The Social Security Disability Insurance program started as a kind of early retirement program at a time when the only benefit Social Security offered was a retirement benefit.) SSDI is paid out of the Social Security Trust Fund; 15 cents of every Social Security tax dollar goes toward the disability trust fund rather then the retirement trust fund. For more information, see our section on SSDI.
SSI stands for Supplemental Security Income and falls under Title 16 of the Social Security Act. SSI, which was created when states' welfare programs for the blind, disabled, and elderly were federalized, is for low-income individuals. SSI disability benefits are not paid out of the Social Security Trust Fund, but out of general funds. Individuals applying for disability benefits who have never worked, or whose work history has not earned them the credits needed to qualify for Social Security Disability Insurance (SSDI), can apply for disability benefits under the SSI program. For more information, see our section on SSI.
Individuals who are found to be disabled and who qualify for SSDI will receive Medicare benefits two years after you start receiving SSDI benefits (or the date you should have started receiving benefits, if your case took along time to process). For the details, see our article on when SSDI recipients get Medicare.
Individuals who are found to be disabled and who are eligible to receive SSI benefits will receive Medicaid benefits immediately. In some states, you need to file a separate application for Medicaid, but in others, your disability application will be a combined application for SSI and Medicaid. Ask a claims representative at your local Social Security office whether you have to file anything to receive Medicaid in your state. For more information, see our article on Medicaid and Medicare for disability recipients.
Some disability recipients can be approved to receive both SSDI and SSI. This is called receiving concurrent benefits. This happens when someone receives a low SSDI payment -- because the individual hadn't worked much in recent years and/or did not make much money by working. When the SSDI payment dips below the federal benefit rate ($735 in 2017), SSI can be used to make up the difference. For instance, say Maria's SSDI monthly check is $350 and she has no other income. She should also receive a monthly SSI check for $403 ($20 of the SSDI income is not counted).
You do not have to request concurrent benefits when you apply for disability. If your income, including your anticipated SSDI payment, is less then the federal benefit rate, Social Security will automatically pay you SSI.
If your state adds a supplemental payment to the federal SSI payment, your SSI check would be bigger. For more information, see our article on state supplemental payments to SSI.