UK self-employed National Insurance calculator: Class 4 and Class 2

If you're a self-employed sole trader in the UK, you pay National Insurance on your profits through Self Assessment. Type in your profits and the calculator works out Class 4 the way HMRC does: 6% on profits between £12,570 and £50,270, and 2% on anything above. It also tells you where you stand on Class 2, which nobody has had to pay since 6 April 2024.

Figures for the 2026 to 2027, 2025 to 2026, 2024 to 2025 tax years, checked against GOV.UK, HMRC's National Insurance Manual and the legislation on legislation.gov.uk on 2026-10-11. Not written by an accountant.

The short answer

• Class 4: for 2026 to 2027, 6% on profits over £12,570 up to £50,270, and 2% on profits over £50,270 (GOV.UK: Self-employed National Insurance rates).
• Class 2: nothing to pay. If your profits are £7,105 or more, Class 2 is "treated as having been paid to protect your National Insurance record" (GOV.UK).
• Below £7,105: you don't have to pay anything, but you can choose to pay voluntary Class 2, £3.65 a week for 2026 to 2027, to protect your National Insurance record (GOV.UK: Voluntary National Insurance).
• How you pay: "Most people pay Class 2 and Class 4 National Insurance through Self Assessment" (GOV.UK), along with Income Tax, which is a separate calculation.

The National Insurance calculator

Pick the tax year and type in your profits from self-employment for that year. It starts with a made-up example: £35,000 of profits in 2026 to 2027.

The example's numbers are made up to show how it works; they aren't typical. Amounts are worked to the penny; your Self Assessment calculation is the final word.

1. Class 4: how it's worked out

The law sets Class 4 as the main Class 4 percentage of profits that exceed the lower limit but don't exceed the upper one, plus the additional percentage of profits above the upper limit (Social Security Contributions and Benefits Act 1992, s. 15). HMRC's manual puts it the same way (HMRC: NIM24045):

• Up to the Lower Profits Limit (£12,570): no Class 4. "If your profits are more than £12,570 a year, you must pay Class 4 contributions" (GOV.UK).
• From the Lower to the Upper Profits Limit (£12,570 to £50,270): the main rate, 6%.
• Above the Upper Profits Limit: the additional rate, 2%, with no cap: "There is no limit on the amount of additional Class 4 NICs payable" (NIM24045).
• Profits here are the trading profits you pay Income Tax on: your self-employed income minus allowable expenses (GOV.UK, s. 15(1)).

In the example above: £22,430.00 of profits is over £12,570, and 6% of that is £1,345.80. Nothing is over £50,270, so that's the Class 4 for the year.

2. Class 2 since 6 April 2024

Class 2 used to be a flat weekly amount that most self-employed people had to pay. The National Insurance Contributions (Reduction in Rates) Act 2023, s. 3 removed the requirement to pay it from 6 April 2024. HMRC: "liability to pay Class 2 NICs no longer exists" (NIM70300). What's left:

• Profits at or above the Small Profits Threshold (£7,105 for 2026 to 2027): you're treated as having paid Class 2 for each week you were self-employed, which protects your National Insurance record for the State Pension and some benefits (s. 11(5A) and (5B), NIM70200). You pay nothing.
• Profits below it, or no profits: you can pay Class 2 voluntarily, at £3.65 a week for 2026 to 2027 (s. 11(6), GOV.UK: rates). HMRC says you can choose to do this "when completing their SA tax return", or outside Self Assessment if you have no profits (NIM70300).
• Contribution weeks run Sunday to Saturday, and "the first week of the contribution year starts on the first Sunday after 5 April"; "some contribution years will include 53 contribution weeks" (NIM70200). By that rule we count 52 weeks in 2026 to 2027, 53 weeks in 2025 to 2026, 52 weeks in 2024 to 2025, so a full year of voluntary Class 2 is £189.80 for 2026 to 2027, £185.50 for 2025 to 2026, £179.40 for 2024 to 2025.

3. Rates and thresholds by tax year

From GOV.UK's table of National Insurance rates and allowances (GOV.UK: Rates and allowances: National Insurance contributions, tables 3.1 and 3.2). The contribution weeks are our count, as above.

Swipe or scroll sideways to see more →

• The Class 4 limits and rates are the same in all 3 years; only the Class 2 figures change. The year before, 2023 to 2024, the main rate was 9% and some self-employed people still had to pay Class 2, so the calculator starts at 2024 to 2025.
• Next year: GOV.UK hadn't published figures after 2026 to 2027 on 2026-10-11. We'll add the next year when it does, not before.

4. HMRC's worked examples

HMRC's manual has two examples, using the 2018/2019 limits (£8,424 and £46,350) and rates (9% and 2%) (HMRC: NIM24051). Run through the same calculator code with those figures, they come out the same as HMRC's:

Those are old rates, shown only because they're HMRC's own worked examples. Since 6 April 2024, the method for someone who's only self-employed is just the two Class 4 steps added together, with no Class 2 step (NIM24153).

5. State Pension age and other exceptions

• Over State Pension age at the start of the tax year: no Class 4 for that year (Social Security (Contributions) Regulations 2001, reg. 91). "A person who attains State pension age during the course of the year of assessment remains liable for Class 4 NICs for the whole of that year" (NIM24510). GOV.UK's example: you reach State Pension age on 6 September 2026, stop Class 4 from 6 April 2027, and pay your final Class 4 bill by 31 January 2028 (GOV.UK: Stop paying National Insurance). Class 2 is no longer treated as paid after you reach it.
• Under 16 at the start of the tax year: no Class 4 (NIM24510).
• Not UK resident for Income Tax in the year: no Class 4 (reg. 91).
• Also employed? Class 1 on your wages is separate. If you pay both, there's an annual maximum that can reduce Class 4; HMRC's manual points to it from NIM24045. The calculator doesn't work it out.

6. Income Tax is separate

• National Insurance is only part of what you owe on your profits. Income Tax is worked out on the same profits after your Personal Allowance, and you pay both through Self Assessment by the same deadlines. This calculator doesn't estimate Income Tax.
• Payments on account cover Class 4 as well as Income Tax. Our UK Self Assessment payments on account guide has a checker for HMRC's two tests and the January and July amounts.

If you'd like the records behind your profits kept in one place, our paid Freelance Billing Kit by Small Rows (US$12, one-time) tracks invoices, payments and expenses, and has an optional UK payments-on-account tab where you type your own figures. It doesn't work out National Insurance; it's a record-keeping tool, not tax advice.

7. Before you pay voluntary Class 2

• Check first. GOV.UK says to check your National Insurance record for gaps and your State Pension forecast, and that "voluntary contributions do not always increase your State Pension" (GOV.UK: Voluntary National Insurance).
• Who can pay Class 2: self-employed people with a gross income of £1,000 or less, or with profits under the Small Profits Threshold (GOV.UK: who can pay). Class 3 is the other voluntary option, at £18.40 a week for 2026 to 2027 (GOV.UK: rates).
• Which rate: paying for the previous tax year, you pay that year's own rate; for any earlier year, the current year's rate (GOV.UK: rates). The calculator mentions this when you pick an older year.
• Deadline: you can usually pay for the past 6 years, by 5 April each year; for 2025 to 2026, by 5 April 2032 (GOV.UK: deadlines).
• Abroad: from 2026 to 2027 you can't pay voluntary Class 2 for time abroad; Class 3 has its own conditions (GOV.UK: if you live or work abroad).

Where the sources differ

We read the pages listed under Sources on 2026-10-11. A few details don't line up neatly; here's how this page handles them:

• An announced rate that never applied. The Autumn Statement 2023 factsheet says the main Class 4 rate would fall "from 9% to 8% from April" (GOV.UK: Autumn Statement 2023 factsheet). A later Act set it at 6% from the same date and says the earlier cut "is to be treated as never having had effect" (National Insurance Contributions (Reduction in Rates) Act 2024, s. 1). GOV.UK's tables show 6% for 2024 to 2025, and the calculator uses that.
• HMRC's rates table stops early. The table in NIM24050 ends at 2024-2025; it has no rows for later years. GOV.UK's rates page and the Act give the later figures (the same limits and rates).
• "Over" or "at" the Small Profits Threshold? The Act says profits "of, or exceeding" the threshold (s. 11(5A)), GOV.UK says "£7,105 or more" (GOV.UK) and HMRC says "at or above" (NIM70300), but the explanatory notes to the 2026 to 2027 regulations call it the threshold "over which" Class 2 is treated as paid. The calculator follows the Act: profits exactly at the threshold count.
• Old examples, old Class 2 rule. HMRC's worked examples (NIM24051) say each person "will also be liable to pay Class 2 NICs". That was the rule in 2018/2019; since 6 April 2024 nobody is liable to pay it (NIM70300).
• 53-week years. GOV.UK gives Class 2 as a weekly rate only. Our week counts follow NIM70200's definition; HMRC's bill or Self Assessment calculation sets the exact amount.

How the calculator works

• Class 4: 6% of the profits between the Lower and Upper Profits Limits for the year you pick, plus 2% of the profits above the upper limit. Each band is rounded to the nearest penny. A loss or zero gives no Class 4.
• Class 2: if your profits are at or above that year's Small Profits Threshold, it's treated as paid; below it, it shows the weekly voluntary rate and the cost of a full year (rate × contribution weeks).
• The State Pension age box sets Class 4 to nil for that year and says Class 2 doesn't apply.
• It doesn't know about the annual maximum for people who are also employed, part years of self-employment, Special Class 4, share fishermen, volunteer development workers, or deferment.

When to talk to an accountant

• you're employed as well as self-employed and your total National Insurance looks high (the annual maximum);
• you're in a partnership, have more than one trade, or your profits include losses carried forward;
• you started or stopped during the year, or your profits are near the Small Profits Threshold and you're deciding whether to pay voluntarily;
• you live or work abroad, are close to State Pension age, or aren't sure whether you're self-employed at all.

Related free resources

• UK Self Assessment payments on account: who has to make them, the 31 January and 31 July amounts, with a checker.
• UK VAT registration threshold checker: your rolling 12-month turnover against the threshold, month by month.
• UK late payment interest calculator: statutory interest when a business client pays late.
• Free invoice generator: an invoice in pounds (or any currency), as a PDF.
• US self-employment tax calculator, if you also work in the US.
• All free tools.

Sources

GOV.UK guidance, HMRC's National Insurance Manual on gov.uk, and legislation.gov.uk, read on 2026-10-11. Rates change each tax year; check the live pages before you rely on them.

• GOV.UK: Self-employed National Insurance rates · Rates and allowances: National Insurance contributions · Stop paying National Insurance (State Pension age) · Autumn Statement 2023: National Insurance factsheet
• Voluntary National Insurance: Overview · Who can pay · Rates · How and when to pay · If you live or work abroad
• HMRC National Insurance Manual: NIM24045 · NIM24050 · NIM24051 · NIM24153 · NIM24510 · NIM70200 · NIM70300
• Legislation: SSCBA 1992, s. 15 (Class 4) · SSCBA 1992, s. 11 (Class 2) · SI 2001/1004, reg. 91 · NICA 2023, s. 2 · NICA 2023, s. 3 · NICA 2024, s. 1 · SI 2026/231 · SI 2025/288

GOV.UK page dates when read: self-employed rates 2015-02-10; rates and allowances 2026-04-06; voluntary National Insurance 2025-01-10; NIM70200 and NIM70300 2024-04-06; NIM24050 2022-11-09.

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