When you apply for benefits you are effectively saying that you have a disability that is expected to last for at least a year. Most applicants will expect that the disability will last considerably longer than that but there is the option to receive benefits to cover a time when you were disabled even if you no longer are. Social Security call that the closed period.
The closed period does apply to both SSDI and SSI although there is a difference in the calculations of back-pay. With all SSDI cases there is a 5 month waiting period from the month of disability onset to the month you receive your check and that is factored into the calculation: a 12 month closed period will only yield 7 months’ worth of backpay. With SSI there’s no waiting period so the same closed period will provide you with 12 months’ of benefits.
To qualify for the closed period you have to have met the criteria for disability for at least 12 months before you returned to working at Substantial Gainful Activity (SGA) levels. In most cases you also have to apply within 14 months of your return to work although Social Security will allow applications up to 36 months after you were no longer disabled if you can show that your delay in filing was caused by an impairment.
While you might make the decision to apply for a closed period of SSDI or SSI as you were disabled for a period of 12 months or more but have since returned to work you can also qualify for the closed period without actively aiming to do so. If your initial application for on-going benefits is still pending when you return to work, instead of dismissing your application Social Security should look to see if you did meet the criteria for the closed period during that time when you were not able to work. Additionally, Social Security may simply decide that although you feel you qualify for on-going benefits you only qualify for benefits for a period of time that has since passed.