The Social Security Administration provides a helpful page on their Web site that updates the amount a person can earn and still be available for disability benefits. This amount, for the various categories, changes each year because it has a cost of living factor built in to the calculations. Here is a statement from the Web site, which goes on to explain the basic 2007 monthly SGA amount is $900.
To be eligible for disability benefits, a person must be unable to engage in substantial gainful activity (SGA). A person who is earning more than a certain monthly amount (net of impairment-related work expenses) is ordinarily considered to be engaging in SGA. The amount of monthly earnings considered as SGA depends on the nature of a person’s disability.