Social Security Questions? Ask a Social Security Expert
The amount you receive each month is based on your average lifetime earnings before your disability began. It is not based on how severe your disability is or how much income you have.
Social Security bases your retirement and disability benefits on the amount of income on which you've paid Social Security taxes—called "covered earnings." Your average covered earnings over a period of years is known as your average indexed monthly earnings (AIME). A formula is applied to your AIME to calculate your primary insurance amount (PIA)—the base figure the SSA uses in setting your benefit amount. The formula consists of fixed percentages of different amounts of income (called "bend points," which are adjusted each year). For example, in 2016, 90% of the first $856 of your AIME was added to your PIA, plus 32% of your AIME from $856 to $5,157, plus 15% of your AIME over $5,157. The amounts are added up to come up with your PIA.
If you do not believe your benefits were calculated correctly then you should speak with your local SSA office.