If you are newly self-employed, National Insurance can feel like a separate, mysterious bill on top of Income Tax. In practice, it is worked out and paid through exactly the same process — your annual Self Assessment tax return — so there is no extra login, separate account or additional deadline to remember.
The two types that apply to you
As a self-employed person, two classes of National Insurance can apply:
- Class 2 — a flat weekly rate, charged once your profits are above the Small Profits Threshold. It counts towards your qualifying years for the State Pension.
- Class 4 — a percentage of your profits above a set threshold, similar in principle to employee NI. This does not build any additional state benefit entitlement.
How it is actually collected
HMRC calculates both classes automatically from the profit figures you enter on your Self Assessment return. The total appears as part of your overall tax bill, alongside Income Tax, and is due on the same 31 January deadline (with a possible second payment on account by 31 July, depending on your bill size).
There is no separate direct debit or standing order to set up specifically for National Insurance — it is bundled into your Self Assessment balance. If you use HMRC's Budget Payment Plan to spread your tax bill across the year, that covers your National Insurance too.
If your profits are low
If your profits fall below the Small Profits Threshold, you will not automatically pay Class 2 National Insurance. However, you can elect to pay it voluntarily — often worthwhile if you want to keep building qualifying years towards your State Pension, since the flat weekly rate is relatively low compared to the value of a protected year.
Working out what you will actually owe
Rather than estimating manually, the fastest way to see your combined Income Tax and National Insurance liability is to run your expected profit through a sole trader tax calculator, which applies the correct 2026/27 thresholds automatically.
See exactly what you'll owe
Enter your expected profit and get your full Income Tax and National Insurance breakdown instantly.
Open Sole Trader Tax Calculator
Frequently asked questions
Do I need to do anything separately to pay National Insurance?
No separate payment process is usually needed. Both Class 2 and Class 4 National Insurance are calculated and collected through your Self Assessment tax return, as part of the same payment you make for Income Tax by 31 January.
What is the difference between Class 2 and Class 4?
Class 2 is a flat weekly amount that helps build your entitlement to the State Pension and other benefits. Class 4 is a percentage of your profits above a threshold, similar in structure to employee National Insurance, and does not count towards state benefits.
What if my profits are below the threshold?
If your profits are low, you may not owe Class 4 National Insurance at all, but you can still choose to pay voluntary Class 2 contributions to protect your State Pension record if your profits fall below the Small Profits Threshold.
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