Another way to look at/understand the SSDI Work History requirements:

 

In general, to get SSDI benefits, you must meet two different earnings tests:

1. A "recent work" test based on your age at the time you became disabled AND
2. A "duration of work" test to show you worked long enough under Social Security

Please note that you must use BOTH of these charts to determine eligibility; counterintuitively, for many younger people the recent work test is longer than the duration of work test.

(For adults disabled before age 22 see Advocacy Tip).

Rules for work needed for the “recent work test”
If you become disabled...	Then you generally need:
In or before the quarter you turn age 24	1.5 years of work during the three-year period ending with the quarter your disability began.
In the quarter after you turn age 24 but before the quarter you turn age 31	Work during half the time for the period beginning with the quarter after you turned 21 and ending with the quarter you became disabled. Example: If you become disabled in the quarter you turned age 27, then you would need three years of work out of the six-year period ending with the quarter you became disabled.
In the quarter you turn age 31 or later	Work during five years out of the 10-year period ending with the quarter your disability began.

Note: the chart below uses "years" for simplicity. But SSA really uses "credits" to determine eligibility. SSA uses work "credits" to determine if you have enough work in such jobs to be eligible for benefits. To earn a credit in 2013 you must earn $1,160 (Historical list). You can earn a maximum of 4 credits a year. You might work all year to earn 4 credits, or you might earn enough for all 4 in a much shorter length of time. (Source)  For more information see: How You Earn Credits- SSA Publication No. 05-10072.

Examples of work needed for the “duration of work" test
If you become disabled...	Then you generally need:
Before age 28	1.5 years of work
Age 30	2 years
Age 34	3 years
Age 38	4 years
Age 42	5 years
Age 44	5.5 years
Age 46	6 years
Age 48	6.5 years
Age 50	7 years
Age 52	7.5 years
Age 54	8 years
Age 56	8.5 years
Age 58	9 years
Age 60	9.5 years

Advocacy tip: adults age 18 and over who were disabled before age 22 may qualify for SSDI on the basis of a parent's work IF a parent is receiving SSDI benefits or is deceased and worked long enough under Social Security. The Adult disabled as a child must meet Social Security's definition of disability for an adult and not be earning more than Substantial Gainful Activity acceptable level of earnings. (see SSA publication: Benefits For Children With Disabilities) See also Dependents' Benefits.