When a person is awarded Social Security Disability Insurance how is it that Social Security can withhold 6 months of pay?

When you are awarded Social Security disability benefits, you do not receive benefits beginning on your onset date. Rather, there is a 5 month "waiting period" before benefits begin. As a practical matter, however, it is often a 6 month waiting period. This is because the waiting period is 5 full months of disability. So if you have partial month, that month simply doesn't count. For example, if you became unable to work on the 2nd day of the month, that whole first month would not count, since it is a partial month of disability. So the effective waiting period can be as long as six months before benefits are due. For SSI benefits, there is no waiting period. Benefits accrue beginning the day you file for benefits. Soure: http://www.socialsecuritydisabilitylawyer.us/blog/2008/07/title-ii-waitin.html