NIM08420 | Earnings Periods: Payments after the employment has ended: Employee paid a week in hand
From HM Revenue & Customs · National Insurance Manual
Regulations 3(5) & (6) of the Social Security (Contributions) Regulations 2001 (SSCR 2001) (SI 2001 No 1004)
Where it is the employer’s practice to keep earnings for one week in hand and, as a consequence, earnings for 2 weeks are paid to an employee when they leave:
split the earnings into respective weekly amounts; and
calculate NICs separately on each amount on a weekly basis.