The term base period is often used in reference to unemployment benefit claims. When an employee files unemployment, a state agency may ask the employer to provide a payroll and work history for the claimant during a specified a base period. Providing this data helps the state unemployment agency determine how much unemployment the employee may have due. The state also uses the base period information to determine which employer’s unemployment account to charge for the unemployment claim.

Most states generally use a standard base period as the benchmark for deciding whether unemployment benefits will be awarded. In almost all states, the standard base period is the amount an employee earned in a 12-month period that includes the first four of five completed quarters. For example, if an employee submitted a claim for unemployment in March 2012, the unemployment office would request information for the base period of January 1, 2011, to December 31, 2011, to calculate eligibility for unemployment compensation.

There are exceptions to the standard base period. Several states also may also use an alternative base period that takes into account more recent work, especially in the case of new or low-wage workers. Some states may use an extended base period to determine unemployment that takes into account wages earned before an illness or injury.

For a chart detailing unemployment compensation laws for each state, refer to the .