HMRC internal manual

National Insurance Manual

NIM10003 - Aggregation of Earnings: More than one employment with different employers: General

Regulation 15, Social Security (Contributions) Regulations 2001

If someone is employed by different employers at the same time and each employer pays them, contributions for each employment are normally calculated separately. However, regulation 15 of the Social Security (Contributions) Regulations 2001 provides for certain circumstances in which the earnings from the different employments should be aggregated, and contributions calculated on the total.