Janke's post was spot on and should help all of you quite a bit. It can take a couple of months to get your back pay. Keep in mind that SSI and SSDI are two different programs within Social Security. SSDI is based on the money a worker pays in Social Security when they were able to work. If someone did not work or did not pay enough into Social Security, then they will draw SSI. The Social Security Administration requires a lot more information from the applicant when they receive SSI. Usually, they interview in person and you must bring in documentation to prove your outgoing bills. If you haven't received your back pay within 90 days, you should go back to your attorney for help with the back pay.