National Insurance is separate from Income Tax. Most employees use Category A, but your payslip category letter and earnings period can change the deduction.
This guide is a planning explanation. Actual payroll deductions depend on your category letter, pay period, employment status, employer setup and HMRC rules.
Category A is common, but it is not universal
Many employees are Category A, but different letters apply for some married women or widows with a valid election, employees over State Pension age, apprentices under 25, veterans and other cases.
A calculator that assumes Category A can be useful for a common estimate, but it should not be treated as a payslip guarantee.
NI uses pay-period thresholds
Employee Class 1 NI is usually calculated using earnings in the pay period, not only annual salary. Monthly, weekly and annualised calculations can therefore look different.
Directors and people with more than one job can have special treatment or separate earnings calculations.
Examples to check on a payslip
Example 1: A monthly salary just above a threshold may show NI on the slice above the threshold, not on the whole salary.
Example 2: A bonus month can create a higher NI deduction because the pay period earnings are higher.
Example 3: A worker over State Pension age may have a different category letter, so a Category A estimate may overstate employee NI.
Included and excluded items
- Included: Gross pay, Pay period, Category A employee NI rate assumption, Monthly or annual planning estimate
- Not included: Employer NI, Director annual earnings method, Non-A category letters, Multiple-employment deferral, Benefits and payroll corrections
- Check before relying on the result: Payslip NI letter, GOV.UK National Insurance rates, Employer payroll team, HMRC when your category seems wrong