The "date last insured" (DLI) is the last date you are eligible to qualify for Social Security Disability Insurance (SSDI). Your DLI depends on when you last worked. (After you stop working, Social Security does not give you an indefinite time to file for disability.)
In order to qualify for SSDI, you must pass the "recent work" test, which means you must have worked five of the past ten years (technically, 20 of the last 40 quarters). (The rules are a bit different if you are under 30; see our article on the required work credits for SSDI.)
Generally, Social Security will look back ten years from the date the applicant filed a disability claim to determine an individual's DLI (this is called the "look back period"). Note that the date that an individual stops working due to disability is not relevant in determining the ten-year look back period; it's the ten years before the application date that counts.
Your DLI depends on the date you stopped working at a job that pays into the Social Security system through FICA taxes. For instance, if you worked up until five years ago, your DLI would be today. If you worked up until four years ago, your DLI would be one year from now. If you haven't worked for six years, your DLI was one year ago. If your DLI has passed, you can't get SSDI benefits. In the same way an auto accident must occur before your auto insurance expires, your disability onset must happen before the date you were last insured (DLI) for disability benefits.
In general, if you apply for SSDI after your DLI has gone by, you'll need to show that the onset of your disability was prior to your DLI. (There is one exception to this rule. If you received a "protective filing date" before you filed your disability application, and the protective filing date is before your DLI, you will still be eligible for benefits.)
Because many disabilities do not have a singular event that causes them, establishing a disability onset date can be difficult, and medical evidence is required to support that onset date. Often an applicant's medical record will not contain enough evidence to show that the onset date was a certain number of years ago. But if you applied for SSDI at an earlier time, sometimes an SSDI lawyer will be able to reopen your old Social Security claim for evidence of an early disability onset date.
If your onset date is determined to have occurred before your DLI, you still have to fulfill the recent work requirement. But in this case, the ten-year look back period will start with your onset date of disability. For instance, if you quit work six years ago because you were in a bad accident, but you didn't apply for SSDI until today, the ten-year look back period would start six years ago. As long as you worked a total of at least five years (20 quarters) in the time period ranging from sixteen years ago until six years ago, you would be insured for SSDI.
If you file a disability claim after your DLI and you can't establish that your disability onset date was before your DLI, you may still be eligible for Supplemental Security Income (SSI) benefits -- if you have low assets and income. The date last insured does not apply to SSI benefits. For more information, see our overview of SSI.