A calendar quarter refers to blocks of three months spread out over the calendar year. The first calendar quarter begins January 1 and ends March 31, the second calendar quarter begins April 1 and ends June 30, the third calendar quarter begins July 1 and ends September 30, and the fourth calendar quarter begins October 1 and ends December 31. A quarter of coverage as used by the Social Security Administration (SSA) is any calendar quarter in which you are insured under the Social Security program. The term quarter of coverage is no longer used by the SSA. Instead, they use Social Security credits, or just credits.
You must be insured under Social Security in order to receive Social Security Disability benefits. As you work and pay Social Security taxes, you earn credits that qualify you for future disability benefits. Credits are based on how much you make. In 2010, you receive one credit per $1,120 of earnings. However, you can earn no more than four credits per year, regardless of the amount of your earnings. Each year the amount of earnings needed to secure a Social Security credit changes and generally more earnings are needed to secure a credit. Credits remain on your government record, even during periods of unemployment.
To receive Social Security Disability benefits, you must have earned at least 20 credits during the last ten years and you must be fully insured. Twenty credits is equivalent to 20 3-month periods of work in which you have paid into the Social Security system and have earned enough money to secure a credit. There are some exceptions to this rule for younger workers.
To be fully insured for purposes of disability benefits, you must have earned at least one credit each year between the time you attained age 21 and the year you become disabled and you must have earned at least six credits.
In general you are considered permanently insured and you will not lose your fully-insured status when you stop working if you have earned the maximum of 40 credits.