What's the difference between SSDI and SSI??

SSDI (Social Security Disability Insurance) 

SSDI is for people who have worked and paid into Social Security.  Because of this, you need so many credits to qualify for it.  If you're 30 and under, it depends on how old you were when you became disabled.  Here is a chart that explains it better than even the SSA website.  If you're 31 and over, then you need 20 credits to qualify.  If you become disabled between 24 and 31 you have to have worked at least half time in the last 10 years.  If you become disabled before age 24, then you had to have worked at least one and a half years in the last three years before your disability. The drawback is that your credits before age 21 don't count toward your SSDI credit requirement.  An example, when I called the SSA and asked about my credits, I had 31 total, 18 in the last 10 years.  I meet the credit amounts for SSDI.  13 of my credits do not apply toward my SSDI credit requirement, although they can be used to calculate my benefit amount if my highest earnings happened during that time.  

I think it's the best of the two programs for a many of reasons.  For one, if you have dependents, they will give you so much on top of your own benefits per child, up to 150% of your benefits.  Remember though, you have a cap on how much you can receive in benefits, based on your work history.  Every families cap is different.  Another benefit is that it doesn't matter how much your spouse earns.  He could make 100k a year, and it won't effect your benefits.  One good thing is that after two years, you're eligible for Medicare.  These are just a few of the benefits you enjoy.   

Remember, there is no minimum benefit amount for either program, however, if your SSDI payment is less than 720, you may also get an SSI payment to bring your benefit up to 720.  

SSI (Supplemental Security Income) 

This program is need based.  In other words, its for people who have not worked enough to get the credits you need to qualify for SSDI.  However, since it is needs based, your household income effects how much you receive.  There is also an asset test, for a single person it's 2,000, for a married person it is 3,000.  Children can receive SSI payments as well, but they must be the disabled party.  SSI does not give auxiliary benefits like SSDI does.