There are several different ‘classes’ of National Insurance (NI):
Class 1 NI contributions are payable if you are employed. Your employer will automatically calculate and deduct Class 1 NI contributions through payroll.
Class 2 NI contributions are treated as paid if your self-employment profits are £6,845 or more in the tax year. If your trading profits are less than this amount, you can voluntarily pay Class 2 NI as these contributions qualify for certain benefits, for example, the state pension. Class 2 contributions are based on a set weekly rate (£3.50 per week for 2025/26).
Class 3 NI contributions are voluntary. You can elect to pay voluntary Class 3 NI if you want to fill any gaps in your NI record.
Class 4 NI contributions are due if your self-employment profits are £12,570 or more in a year. Class 4 NI is payable at a rate of 6% for the 2025/26 tax year on your profits between £12,570 and £50,270 and 2% on profits over £50,270.
If you are self-employed, you potentially pay two kinds of NI, Class 2 and Class 4. Most people pay Class 2 and Class 4 contributions through their tax return.
You stop paying Class 2 NI when you reach State Pension age and stop paying Class 4 NI from 6 April after you reach State Pension age.
If you are both employed and self-employed, there is an interaction between each NI class as there is a maximum amount of NI an individual can pay. These calculations can prove complicated, therefore if you are in this position, you should seek professional advice.