If you are found disabled, the judge has to determine the date when you became disabled. The date determined is based on when you stopped working, the strength of medical evidence, and your age. Once the judge determines when you became disabled, social security will then decide the back pay. Social security can only pay one year prior to the date of application.
There is also a five month waiting period once you have been found disabled. This means you have to wait five months before the disability benefits will kick in. Monthly benefits are based upon how much you have paid in to it over the years. Social Security disability is paid from the date on the application so do not wait around to apply because you are not going to get back pay for years prior. The payment center is then going to send out a notice of award that includes information on the total awarded back pay, when you should expect your check each month, and how much it should be.