The short answer
First, you must be insured: enough work credits, earned recently enough. Second, you must meet Social Security's definition of disability, which is strict - a condition expected to last at least 12 months or end in death, preventing work above $1,690 a month in 2026. Earnings above that figure end a claim before the medical evidence is read.
Two tests, decided separately
SSDI is insurance, paid for by the Social Security taxes taken out of your wages. That is what separates it from SSI, which is needs-based and does not ask about your work history. For SSDI, a work record that is too short or too old ends the claim no matter how severe the condition.
The two tests are assessed by different people. A Social Security field office checks your insured status from your earnings record; a state Disability Determination Services office decides the medical question. A claim can be denied at the first stage without a doctor ever reading the file.
Work credits: long enough, and recently enough
You earn one work credit for each $1,890 of covered earnings in 2026, up to four a year - so $7,560 of earnings buys a full year's credits however they fell across the months. The number you need depends on your age when the disability began.
For anyone 31 or older there are two requirements at once: enough credits overall, which works out as your age at onset minus 22, capped at 40; and 20 credits earned in the 10 years before onset. That second test is what catches people who worked for decades and then had several years out of the workforce before becoming ill. Under 31 the rules are gentler - someone disabled before 24 needs only six credits from the previous three years.
Substantial gainful activity is a gate, not a guideline
If you are working and earning at or above $1,690 a month in 2026 - $2,830 if you are statutorily blind - Social Security generally finds you are engaged in substantial gainful activity and denies the claim at step one. The medical evidence is not weighed. This figure is gross earnings from work, not household income and not unearned income.
Some earnings can be discounted. Impairment-related work expenses, and subsidies where an employer pays you more than the work is worth, can be subtracted before the comparison is made. If you are working at all while claiming, this is worth raising explicitly rather than leaving it to be noticed.
The five questions the medical decision asks
The medical review is a fixed sequence. Are you working above the substantial gainful activity level? Is your impairment severe and expected to last at least 12 months or result in death? Does it meet or equal one of the conditions in Social Security's Listing of Impairments? If it does, you are approved there; if not, the review continues.
The last two questions are where most claims are actually decided. Can you still do work you have done in the past 5 years? And if not, can you adjust to any other work that exists in significant numbers, given your age, education and work experience? Age matters a great deal at that final step - the rules apply a different standard to someone over 50 than to someone of 30 with the same impairment.
Approval is not the end of the work rules
Once benefits begin, you can test your ability to work without losing them straight away. A trial work period lets you work for up to nine months - any month with earnings over $1,210 in 2026 counts as one - with full benefits throughout, whatever you earn.
After that comes a 36-month extended period of eligibility, during which benefits are paid for any month your earnings stay below the substantial gainful activity level. There is also a five-month waiting period at the start: SSDI is not payable for the first five full months after the date disability began.
What our calculator works out
Our SSDI calculator checks the part that can be checked: whether your earnings history gives you enough work credits, whether enough of them fall in the recent-work window for your age, and whether your current earnings are above the substantial gainful activity level that would end a claim at step one.
What this does not tell you
The medical decision is not modelled here and cannot be. Whether your condition meets Social Security's definition of disability is decided by a state Disability Determination Services office from your medical records, and nothing on this site predicts that.
The credit estimate uses the earnings you enter. Social Security decides insured status from its own record of your covered earnings, which may differ - it is worth checking your earnings record in your my Social Security account before you rely on an estimate.
Official sources
- Social Security Administration - Disability benefits: how you qualify
- Social Security Administration - How you earn credits
- Social Security Administration - Substantial gainful activity
- Social Security Administration - Disability evaluation under Social Security (the Blue Book)
- Social Security Administration - Working while disabled
What you can do next
Check your insured status first, because it is the test you can verify today and the one that ends claims fastest. If the work credits are there, gather the medical evidence before applying rather than after - the completeness of the initial file is the single biggest thing within your control.