The alleged onset date is very simply the date on which the claimant alleges his or her disability began. This onset date is usually included in the original application filed by the claimant seeking disability benefits. The alleged onset date is important because potentially it will be used to determine how much the claimant is due or can receive in past benefits and backpay. In a case where an administrative law judge or a disability examiner has approved the alleged onset date, that date will then become the established onset date. The established onset date will then be used to determine what the claimant might be entitled to receive in backpay and benefits from the social security disability system.