Class 3 NICs: time limits for paying class 3 NICs: applying the higher rates
Section 13(6), Social Security Contributions and Benefits Act 1992
If Class 3 NICs are paid after the end of the second tax year after the one for which they are being paid, they should normally be paid at a higher rate. Each contribution is payable at the highest Class 3 rate applicable in the period from the week the contribution was due to the date the contribution is paid. This does not apply
- for the years 1996/97 to 2001/02 when the special provisions at NIM25043 apply, or
- in the circumstances described at NIM25030.
Regulation 64, Social Security (Contributions) Regulations 2001
If HMRC invites payment of Class 3 NICs in the last month of a tax year and they are paid within one month of the request they will remain payable at the rates which applied at the time the payment was requested.