Self-employed people deal with two kinds of National Insurance. They are easy to mash together because both say "Class" and both sit on the Self Assessment return. They do different jobs.
Class 4 is a tax-like charge on profit. You pay it. Class 2 is mostly about keeping your National Insurance record complete for the State Pension. For most people with decent profit in 2026/27, Class 2 is treated as paid and there is no weekly cash amount on the bill.
Both are worked out on profit, not turnover. See turnover or profit if that split is still fuzzy.
Class 4: the one that costs money
For 2026/27 you pay Class 4 on self-employed profit of:
- 6% between £12,570 and £50,270
- 2% on profit above £50,270
Nothing below £12,570. It is collected through Self Assessment with your Income Tax, not as a separate invoice during the year.
A sole trader in England with £30,000 profit and no other income pays £1,045.80 of Class 4 (6% of £17,430). That is the figure the calculator shows alongside the Income Tax.
Class 4 does not give you a qualifying year for the State Pension. It is just a charge.
Class 2: the one that protects your record
The Class 2 rate for 2026/27 is £3.65 a week. You only actually choose to pay it if your profit is under £7,105.
If profit is £7,105 or more, Class 2 is treated as paid. You do not send HMRC £3.65 a week, and you still get the qualifying year on your National Insurance record, the same as if you had paid it. That change has been in place since April 2024. Older articles and forum posts that talk about a flat Class 2 "stamp" on every Self Assessment bill are out of date.
Under £7,105, nothing is treated as paid. You can pay Class 2 voluntarily to fill the year. Check your State Pension forecast first. If a PAYE job already gives you a qualifying year, you may not need to.
Three profit levels
| Profit | Class 2 | Class 4 |
|---|---|---|
| £6,000 | Not treated as paid. Voluntary £3.65 a week if you want the year. | None |
| £10,000 | Treated as paid. No cash charge. | None (still below £12,570) |
| £30,000 | Treated as paid. No cash charge. | 6% on £17,430 = £1,045.80 |
The jump that surprises people is not Class 2. It is crossing £12,570, when both Income Tax and Class 4 start at once.
If you also have a job
Class 1 comes off your wages. That is a third class, and it is the one that usually gives employees their qualifying year.
It does not cancel Class 4 on the self-employed profit. A small side profit under £12,570 often has no Class 4. A larger one is charged in full on that profit, with its own £12,570 floor. Employed and self-employed at the same time has the worked version.
How you pay
Most people pay both through Self Assessment. There is no monthly NI Direct Debit for ordinary sole traders.
A few jobs have odd Class 4 rules (examiners, some ministers, some landlords). If that is you, GOV.UK's self-employed NI page flags it. For a plumber, a designer, a tattooer, the table above is the whole picture.
What to set aside
Class 4 is why the "save 25% of profit" rule is higher than the 20% basic rate. 20% Income Tax plus 6% Class 4 is 26% on the slice between £12,570 and £50,270. How much tax to save is the habit. Do not budget for a weekly Class 2 charge on top unless your profit is under £7,105 and you have chosen to pay it.