What are NI categories and when do I override?

NI categories supported

Cat	Use	Why
A (default)	Standard employee, aged 22+	Most cases
B	Married woman with reduced-rate election (pre-1977 elections only)	Legacy
C	Above State Pension age, OR director paid only above the PT	No employee NI; employer NI still due
H	Apprentice under 25	Employer NI saving — 0% to UEL
J	Has deferred NI in another job	Employee NI deferred
M	Under 21	Employer NI saving — 0% to UEL
V	Veteran in their first year of civilian employment	Employer NI saving — 0% to UEL
Z	Under 21 with deferred NI in another job	Combo of M + J

When to override

Override on the employee detail page > Employment tab > NI category. Common cases:

• Hire an under-21 → set M (employer NI saving for tenant)
• Hire an apprentice under 25 → set H
• Director takes annual salary → set C and toggle Is director for the annual cumulative method
• Employee turns 21 → switch from M to A on their birthday (manual today; automated in a future polish)

Director annual method

For directors, NI is calculated annually cumulatively rather than per-period. The toggle is the Is director toggle on the Employment tab. The engine picks up the flag and uses the annual method automatically. Convenient for variable-salary directors (e.g. salary + dividends pattern).