National Insurance Contributions come in 4 basic types. Depending on your work and other circumstances, you may have to pay more than one type:
Class 1 NICs
These are the National Insurance Contributions paid by most UK employees. They’re taken automatically from your earnings by your employer, through the PAYE system. You keep paying Class 1 NICs until you hit the State Pension age.
Class 2 NICs
Self-employed people don’t generally use the PAYE system to pay their tax. Instead, they file Self Assessment tax returns each year to tell the taxman about their profits and business expenses. Since they don’t have an employer, they pay Class 2 NICs rather than Class 1, which are handled through the Self Assessment system.
Things changed a lot for the self-employed with the 2024 Spring Budget, which saw the abolition of Class 2 NICs. However, self-employed people with total profits under £6,725 a year can chose to keep paying NICs, to make sure they're still entitled to the state benefit they cover.
Class 3 NICs
If you’ve got gaps in your National Insurance history, you can make voluntary NIC payments to plug them. These voluntary payments are called Class 3 NICs. They can make good sense if you’re looking to make sure you qualify for things like the maximum State Pension rate.
Class 4 NICs
Class 4 National Insurance Contributions are another kind of payment made by the self-employed. If your profits from self-employment are high enough, you pay Class 4 NICs as well as Class 2.
Things get slightly more complicated if you’ve got more than one kind of income. Employees who also have some self-employment income could find themselves paying Class 1 NICs through the PAYE system and (until their abolition on the 6th April 2024) Class 2 NICs through Self Assessment. If their self-employment profits are high enough, they’ll pay Class 4 NICs as well.