The "alleged start date" decides when you become eligible for disability payments and how far back you will be paid.
If you were handicapped before applying for SSDI, you may get retroactive benefits for up to 12 months from the day you applied. To be eligible for a full year of backpay, you must have been handicapped for at least 17 months prior to the day you applied, because there is a five-month waiting period after being incapacitated during which benefits are neither paid or payable. (There is no retroactive compensation for SSI; if you are granted, benefits will begin the month you apply.)
Onset Day or AOD for SSDI
The amount of backpay you can get for past-due benefits is affected by your disability start date. Assume you applied for SSDI on December 1, 2021, claiming that your disability began on September 1, 2021. Assume your benefits are approved by the Social Security Administration (SSA) on December 1, 2022. If the SSA agreed to your 9/1/2021 start date, you would be eligible for backpay from 2/1/2022 (five months after your 9/1/2021 AOD) until 12/1/2022. (The date of your approval).
If, on the other hand, the SSA disagreed with your onset date and ruled that you were not disabled until 2/1/2022, you would not be eligible for benefits until 7/1/2023 (five months after your onset date of 2/1/2022). This might result in thousands of dollars in backpay.
Because you must be handicapped for 12 months (or be expected to be affected for 12 months) to be eligible for disability payments, the start date can also influence whether or not your claim is approved. The day of onset is the start date for this 12-month durational criteria.
How Can the SSA Change Your Onset Date?
If the Social Security Administration disagrees with the date you claim you were disabled, it may calculate an onset date that is later than you believe. The onset date determined by the SSA is referred to as the established onset date (EOD) rather than the claimed onset date (AOD). However, the SSA must have opposing medical evidence to show that your claimed date is erroneous and that its EOD is valid.
The SSA will determine your EOD based on your AOD, when you last worked, and the medical evidence.
If the SSA learns that an applicant returned to work after applying for benefits for a length of time, the agency will most likely issue the applicant an EOD stating the date the applicant last worked at this job. (However, an applicant who applies for benefits because of an inability to work and then attempts and fails to return to work may be able to claim a "unsuccessful work attempt" and keep the original supposed start date.)
What to do if the SSA Changed Your Onset Date?
If the SSA changes your AOD to a later EOD, you can challenge the new established onset date by seeking a review of the EOD from Disability Determination Services (DDS). If you are already at the hearing stage, you can request that the EOD be considered by an administrative law judge or the Appeals Council. However, if you contest the commencement date, the DDS or SSA may review the disability determination and potentially revoke your clearance. If you have been granted benefits, you should seek a disability attorney for help with an EOD appeal.
When Social Security changes your AOD to a later EOD, it may still be more than 17 months before the day you applied for disability benefits. The change in date is immaterial in this case since you cannot be paid backpay benefits for more than 12 months previous to your application date (plus the five-month waiting period).
If you are approved for benefits and Social Security or DDS (either an administrative law judge or a disability claims examiner) concludes that your disability began at the time you applied, the AOD is converted to the EOD.