NIM08230 - Earnings Periods: Employee earns a fee for each session they work: Separate fee paid for each session worked
Regulation 4 of the Social Security Contributions Regulations (2001) (SSCR 2001) (SI 2001 No 1004)
If an employer pays an employee a separate fee for each session they work, the earnings period is the length of the session or a week if that is longer. If the employer makes more than one payment at different times in the same week, work out NICs separately on each payment.
See NIM09910 if the employee is an irregular harvest worker.