Applying for, and receiving, Social Security benefits can take a very long time. For that reason, the Social Security Administration will cover your benefits from the time you applied until the time you are approved retroactively. They will also sometimes cover your benefits for up to a year before you applied, depending upon your exact situation.
Most of the time, you will receive some backpay. Social Security is a complex system and, because of this, the backpay element does have to be included within the system itself.