McKenna Collins LLP public accounting firm employs 10 full-time professionals who provide services to clients. All professional labour compensation is traced directly to clients on a per professional labour-hour basis. Any other costs are included in a single indirect-cost pool (same as overhead) and allocated to individual clients according to billable professional labour-hours.

Operating costs and data for the year included the following:

EstimatedActual

Overhead (indirect) costs$1,000,000$1,200,000

Number of billable professional labor-hrs40,00050,000

Total professional compensation750,000750,000

How do I explain qualitatively and quantitatively (in as much detail as possible) the source(s) of the overapplied overhead cost?