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HMRC internal manual

National Insurance Manual

Class 2 National Insurance contributions: General Information: Class 4 liability – section 15 of the Social Security Contributions and Benefits Act 1992 (SSCBA)

Section 15 of the Social Security Contributions and Benefits Act 1992 and Section 15  of the Social Security Contributions and Benefits (Northern Ireland) Act 1992

Chapter 2 of Part 2 of the Income Tax (Trading and Other Income) Act 2005

Self-employed earners, whose profits or gains are derived from the carrying on or exercise of one or more trades, professions or vocations and which are chargeable to income tax under Chapter 2 of Part 2 of ITTOIA 2005 (formerly Cases I and II of Schedule D of the Income and Corporation Taxes Act 1988) pay Class 4 NICs. Class 4 NICs are already assessed and collected (along with income tax) through the Self Assessment system.

From the 2015 to 2016 tax year, the profits used to determine whether a Class 2 NICs liability exists are those profits which are already used for Class 4 NICs purposes under section 15 SCCBA 1992.

Class 4 NICs are payable in addition to any Class 2 NICs due.