NIM10011 - Aggregation of Earnings: Calculating NICs: General
Once it has been established that earnings fall to be aggregated, NICs are calculated based on total earnings received from the respective jobs, i.e. the total earnings received are treated as being a single payment of earnings for a single employment. The employer must use the earnings band and percentage rates relevant to the aggregated earnings to calculate NICs.
Once the earnings period in which the earnings fall to be assessed is determined, all of the earnings received in that period should be assessed using the rates and thresholds in force for that earnings period.
For example, Peggy has two jobs with the same employer; a monthly paid one and a weekly paid one. NICs should be assessed on the shortest earnings period, i.e. weekly. For most weeks the weekly pay is the only one received but every 4 or 5 weeks the monthly pay should be added to the weekly pay and the NICs assessed using a weekly earnings period.