NIM24003 - Special Class 4 NICs: calculation of earnings

Regulation 105 of the Social Security Contributions Regulations 2001 (SI 2001 No. 1004)

Earnings for the purposes of Special Class 4 NICs are the same as those for the purposes of Class 1 NICs (see NIM02000 onwards). However, the NICs payable are calculated at the same percentage rate as ordinary Class 4 NICs.