Excess wages are the portion of wages paid in a quarter that are above the yearly taxable wage base.

In the examples below, $13,000 is the taxable wage base that is used to calculate excess. For a more detailed example, this site has a demonstration of a business′ excess wage calculations for each quarter in a year. 

1.    John Smith
The amount of excess wages in any quarter depends on the total wages the worker has earned in the year. Once a worker earns as much as the taxable wage base ($13,000), anything earned after that is excess wages. However, you report only the excess wages earned by the employee in a quarter, so an employee's excess wage amount is never more than the wages for the quarter.

2.    Jane Doe
Jane Doe has excess wages in the second quarter because she earned wages above the taxable wage base ($13,000). She had no wages in the third quarter, so she had no wages in excess of the taxable wage base that quarter. In the fourth quarter, all Jane Doe's wages were excess wages (when an employee has earned more than the taxable wage base, the wages in subsequent quarters will all be excess wages).