Check the SSA website for specifics. You must earn above a certain amount in a quarter to earn a credit. This increases each year. For instance, if you earned $1,000 each quarter this year, you would not get any credits for work using this year's amounts. Also, up to age 24 you need 6 credits three of which must been in the last 3 years. As you get older you need more credits to qualify and more of these credits must be earned during the last 10 years.

Finally, the amount of SSDI depends upon how much you earned.

The SS earnings and whether you have sufficient credits to qualify for disability appears on the SS statement that used to be mailed to everyone who contributes to SS but now it is only available online.

Hope this helps.