A closed period of disability has a definite beginning and ending date for the claimant's disability, and has to last at least 12 months. In a closed period of disability case, the date the individual became unable to work (or the alleged onset date) "opens" the period of disability, and the date you became able to work "closes" the period of disability. If a claimant's physical or mental disability improves and they are able to return to work they may still meet the disability "durational requirement," and may still qualify for a closed period of disability and still be entitled to Social Security disability benefits.