I'm not sure the $900 min for SSDI is right. Both my husband and I recieve it and neither of us gets that amount. In fact, I get less than what someone on SSI gets due to the fact that when I worked I earned very low wages. I was going to college and working at mostly min. wage jobs which back then was very low. I believe they go by how much you paid into the system. Also, you get paid monthly. At least with SSDI you get your check on a Wed and which Wed is determined by your last name. They used to pay on the 3rd of each month (I still get mine then) but have changed it.