The Trial Work Period is the nine trial work months occurring within a five-year window when you receive full Social Security Disability Insurance (SSDI) monthly benefits and work. These work months can be one right after the other (consecutive) or occur one at a time (non-consecutive.) The trial work months add up to what Social Security calls a Trial Work Period only if they all occur within five years (60 months) of each other. Social Security calls this the Five-Year Window. The Extended Period of Eligibility (EPE) is the 36 consecutive months which start at the end of the Trail Work Period. Different rules apply during this period.
In the Extended Period of Eligibility, any month in which gross earnings (income before taxes) at least $900 (for 2007), your wages are at what Social Security calls Substantial Gainful Activity (SGA). The SGA earnings for blind beneficiaries is different, in 2007, SGA for the blind $1,500.
The first time you have wages at the Substantial Gainful Activity (SGA) level (or higher) during the Extended Period of Eligibility or after this period, you receive a 3-monthgrace period in which you will continue to receive the full SSDI benefit regardless of wage amounts.
During the 36 consecutive months of the Extended Period of Eligibility when your gross earnings are $900 or more (SGA), you are not entitled to a benefit check for that month. If gross earnings fall below SGA or you stop working, you are again entitled to a full monthly benefit payment. There are no new application or waiting period when earnings fall below Substantial Gainful Activity levels. At the end of the 36-month Extended Period of Eligibility, if you continue or begin to earn Substantial Gainful Activity (or more) per month, your SSDI claim will end.
For the five years after this Extended Period of Eligibility, if your earnings fall below Substantial Gainful Activity due to your disabling condition, you may request to be re-instated without a new application. The provision is called Expedited Re-Instatement to Social Security benefits.
See this explanation of the SSDI work rules for further details.