A worker who has worked long enough and recently enough (based on "quarters of coverage" within the recent past) to be covered can receive disability benefits. These benefits start after five full calendar months of disability, regardless of his or her age. The eligibility formula requires a certain number of credits (based on earnings) to have been earned overall, and a certain number within the ten years immediately preceding the disability, but with more-lenient provisions for younger workers who become disabled before having had a chance to compile a long earnings history. The worker must be unable to continue in his or her previous job and unable to adjust to other work, with age, education, and work experience taken into account; furthermore, the disability must be long-term, lasting 12 months, expected to last 12 months, resulting in death, or expected to result in death.[24] As with the retirement benefit, the amount of the disability benefit payable depends on the worker's age and record of covered earnings. Supplemental Security Income (SSI) uses the same disability criteria as the insured social security disability program, but SSI is not based upon insurance coverage. Instead, a system of means-testing is used to determine whether the claimants' income and net worth fall below certain income and asset thresholds. Severely disabled children may qualify for SSI. Standards for child disability are different from those for adults.