In 1974, the Social Security Administration was given the job of administering the brand new Supplemental Security Income program when the federal government took over the previous state programs that provided assistance to the low income elderly and disabled. My own grandmother finally had some money to live on in the last few years of her life since neither she nor my grandfather had ever paid any Social Security taxes since my grandfather's work in agriculture was not covered by Social Security before 1951.

SSI is a safety net for the neediest of the disabled and elderly. As an "entitlement" program, no one "pays into" SSI. It is standard practice in Social Security offices for the interviewer to take a claim for both SSI and SSDI. The decision that a person is disabled is the same for both programs, so SSI cannot pay benefits when a claimant is found not disabled. SSI does not have a waiting period after onset date before benefits begin. SSDI does have a five month waiting period after onset date. SSI is not retroactive before the application is filed. SSDI can be 12 months retroactive before the application is filed if the onset date is in the past.

To qualify for SSI, your income, resources and living arrangements have to be verified by SSA. It can be quite invasive because the agency has to know a great deal about your personal and private business for as long as you get a check. SSI can change amounts every month. SSI can start and stop, go up and down for a variety of reasons. Your spouse's money can determine whether or not you get SSI. You have to pretty much exhaust your assets down to $2000 to qualify for SSI. The amount of the SSI check depends upon your income and living arrangements.

Disabled children who have never paid Social Security taxes can get SSI benefits if the parents have limited income and resources. Certain non-citizens who are recent or long term immigrants who have never paid Social Security taxes can get SSI benefits. US born adults who have never or barely have held a job can get SSI benefits. None of the SSI payments come from the Social Security 'trust funds'. The money can be federal and state (depending upon your state's criteria). The claimants have to meet the income, living arrangement and resource criteria.

To get SSDI you have to pay Social Security (FICA, OASDI) payroll taxes for enough years and be found disabled. There can be an offset for worker's comp or other public disability benefits. Sometimes your dependent family members can get benefits - not always. But it is not a needs based program. There are no limits on the amount of other unearned income (pension, rental, dividend, interest) income you can make. There are no limits on how much savings you can have or how much property you have, or how much money your spouse makes. The amount of the SSDI check is directly determined by the amount of your lifetime earnings and how much you paid into the program.

Your local SSA office takes claims on both programs and they will err on the side of taking a claim and denying it rather than not take a claim when they should. Each case is different so it is difficult to explain why it is often a good idea to take both SSI and SSDI. Mostly, it would be for the person who has worked just enough to have enough credits for SSDI but really has no other assets. Also, some people need medical coverage so badly that they want to qualify for Medicaid which comes with SSI.

The SSI does have to be "paid back" or is offset from the retroactive SSDI benefits when the SSI would have been less in the retroactive period if the SSDI had been paid on time instead of retroactively. That is called windfalloffset. It is not necessarily a dollar for dollar pay back. Every case is different. The windfall offset can be a complex complication and often waiting for it to be completed bogs down the processing of the retroactive SSDI benefits.

I know this is long, but I think it is helpful information.