SSDI is Social Security Disability Insurance - The monthly SSDI is based on your earned work credit you earned in lifetime. The higher credit you get, the more $$ you get.
SSI is Supplemental Security Income - The amount is the same nationwide. However, many states add money to the benefit.
When I was young adult without job and was in college, I had both SSDI/SSI - it helped but not enough, I think it was like around $500/mo since I didnt have any earned work credits. Today, if I claimed SSDI, it probably would be neighbor of $1500 to $2000 due to 10+ years of full time job.
