Class 4 National Insurance Calculator

How the Class 4 National Insurance Calculator Works

This calculator works out exactly how much Class 4 National Insurance you owe on your self-employment profits for the 2025/26 tax year (6 April 2025 to 5 April 2026). Class 4 NI is the profit-based National Insurance that sole traders and partners pay alongside their income tax through the annual Self Assessment tax return. Enter your annual taxable profit, the figure left after you have deducted all your allowable business expenses and capital allowances, and the calculator instantly applies the two Class 4 bands to give you a precise figure.

The calculation is a simple two-band model. For 2025/26 you pay nothing on the first £12,570 of profit (the Lower Profits Limit), then 6% on the slice of profit between £12,570 and £50,270 (the Upper Profits Limit), and finally 2% on every pound of profit above £50,270. There is no upper cap on the 2% band, so it continues indefinitely no matter how high your profits are. The 6% main rate was reduced from 8% on 6 April 2024, so if you are comparing against older guidance you may see the higher historical figure.

If you are over State Pension age, set the dropdown to "Yes". You stop being liable for Class 4 NI from the start of the tax year following the one in which you reach State Pension age, so the calculator will correctly return £0 of Class 4 NI even though you still owe income tax on the same profits. The result panel breaks your liability down band by band, shows your effective Class 4 rate as a percentage of total profit, and explains your Class 2 position so you know whether your State Pension record is protected.

For a fuller picture of all the National Insurance classes, including employee Class 1 and employer NI, use our main National Insurance Calculator. If you want to combine your Class 4 NI with your income tax and Class 2 position in one go, the Self Assessment Calculator brings everything together. Employees who pay Class 1 instead can use the Class 1 NI Calculator, and you can browse the full range of tools on our all calculators page.

Worked Example: £40,000 Self-Employed Profit

The clearest way to understand Class 4 National Insurance is to walk through a real calculation. Suppose you are a self-employed graphic designer with taxable profits of £40,000 for the 2025/26 tax year after deducting your allowable expenses. Here is exactly how HMRC works out your Class 4 NI:

• Step 1 — Profit below the Lower Profits Limit: The first £12,570 of profit is free of Class 4 NI. NI in this band = £0.
• Step 2 — Profit in the 6% main band: Your profit of £40,000 is below the Upper Profits Limit of £50,270, so the whole amount above £12,570 falls in the 6% band. Profit in band = £40,000 − £12,570 = £27,430. Class 4 NI = £27,430 × 6% = £1,645.80.
• Step 3 — Profit in the 2% upper band: Because your profit does not exceed £50,270, no profit falls into the 2% band. NI in this band = £0.
• Total Class 4 NI for the year: £0 + £1,645.80 + £0 = £1,645.80.
• Effective Class 4 rate: £1,645.80 ÷ £40,000 = 4.1% of total profit.

Now consider a higher earner: a self-employed consultant with £70,000 profit. The 6% band is fully used (£50,270 − £12,570 = £37,700 × 6% = £2,262.00) and the remaining profit crosses into the 2% band (£70,000 − £50,270 = £19,730 × 2% = £394.60). Total Class 4 NI = £2,262.00 + £394.60 = £2,656.60, an effective rate of just 3.8%. Notice how the effective rate falls as profits rise, because the 2% upper band is much lighter than the 6% main band. These figures match the official HMRC rates published on the self-employed National Insurance rates page on GOV.UK.

Class 4 National Insurance Rules That Matter for 2025/26

Class 4 National Insurance is one of two National Insurance contributions that self-employed people deal with, and it is the one based on the size of your profits. Understanding the rules below will help you plan your tax bill, budget for your Self Assessment payments, and avoid common mistakes.

The Two-Band Structure

Class 4 NI uses two thresholds. The Lower Profits Limit (LPL) is £12,570 for 2025/26, aligned with the income tax Personal Allowance and the Class 1 Primary Threshold. The Upper Profits Limit (UPL) is £50,270, the same as the higher-rate income tax threshold and the Class 1 Upper Earnings Limit. The main rate of 6% applies between these two limits, and a reduced 2% rate applies above the UPL. The Government has confirmed that the UPL will remain frozen at £50,270 until the 2027/28 tax year, so the band where you pay the full 6% will not widen with inflation in the meantime.

Class 4 Is Calculated on Profit, Not Turnover

A critical point that trips up many sole traders is that Class 4 NI is charged on your taxable profit, not your turnover or your drawings. Taxable profit is your business income minus your allowable expenses, capital allowances, and any trading losses brought forward. The same profit figure is used for both your income tax and your Class 4 NI calculation, which is why both appear together on your Self Assessment return. Class 4 NI itself is not an allowable deduction, so you cannot reduce your profit by the amount of NI you pay.

Class 2 NI and the 2024/25 Change

From the 2024/25 tax year, the way Class 2 works changed significantly, and this affects how you should think about your overall self-employed NI. Previously you paid a separate weekly Class 2 charge if your profits were above the Small Profits Threshold. Now, if your profits exceed the Small Profits Threshold of £6,845 (2025/26), you are treated as having paid Class 2 NI without actually being charged it. This means you continue to build entitlement to the State Pension and certain benefits at no cost. If your profits are below £6,845, you are not required to pay anything, but you can choose to pay voluntary Class 2 contributions at £3.50 per week (£182 per year for 2025/26) to keep your State Pension record complete. HMRC explains this in its self-employed National Insurance rates guidance.

Class 4 Does Not Build Any Entitlement

It is important to understand that paying Class 4 NI gives you nothing in return in terms of benefits. Unlike Class 1 (employees) and Class 2 (self-employed), Class 4 contributions do not count towards the State Pension, Maternity Allowance, or any other benefit. Class 4 is, in practical terms, simply an additional tax on self-employment profits. Your State Pension entitlement as a self-employed person comes entirely from Class 2 (or the deemed Class 2 credit you now receive when profits exceed the Small Profits Threshold), so it is well worth checking that you are credited correctly each year.

State Pension Age and Class 4

You stop being liable for Class 4 NI from the start of the tax year after the one in which you reach State Pension age (currently 66 for both men and women). So if you reached State Pension age during 2024/25, no Class 4 NI is due on your 2025/26 profits. You do, however, continue to pay income tax on your profits for as long as you trade. You can confirm your own State Pension age using the GOV.UK State Pension age tool.

How and When You Pay

Class 4 NI is collected through Self Assessment, not through any separate process. When you submit your tax return, HMRC automatically calculates your Class 4 NI from the profit figure you declare and adds it to your income tax bill. The balancing payment for a tax year is due by 31 January following the end of that year, and if your bill is large enough you will also make payments on account on 31 January and 31 July towards the following year. If your actual profits turn out lower than the payments on account assumed, you can claim to reduce them, and any overpaid Class 4 NI is refunded through your return.

Partnerships and Multiple Trades

If you are a partner in a business partnership, you pay Class 4 NI on your individual share of the partnership's profits, in addition to any profits from other self-employment you carry on. Where you have more than one trade, your profits are added together and a single Class 4 calculation is applied across the combined figure using the same £12,570 and £50,270 thresholds. There is an annual maximum amount of NI a person can be required to pay across all classes; if you also have employment income subject to Class 1 NI, you may be able to defer or reclaim some Class 4 NI to avoid overpaying.

Sources: Self-employed National Insurance rates (gov.uk), Rates and allowances: National Insurance contributions (gov.uk). Last verified: June 2026.

How Class 4 NI Fits With Income Tax and Class 2

For a typical sole trader, three deductions come out of profits: income tax, Class 4 NI, and (historically) Class 2 NI. Understanding how they interact helps you see your true marginal rate. On profits between £12,570 and £50,270, you pay 20% income tax plus 6% Class 4 NI, a combined marginal rate of 26%. On profits above £50,270, you pay 40% income tax plus 2% Class 4 NI, a combined marginal rate of 42%. These are the headline rates that matter when you are deciding whether to make a pension contribution, invest in equipment, or bring forward expenses to reduce a profitable year.

Consider Priya, a freelance consultant with £45,000 of profit. Her income tax is 20% on the slice above the £12,570 Personal Allowance: (£45,000 − £12,570) × 20% = £6,486. Her Class 4 NI is (£45,000 − £12,570) × 6% = £1,945.80. Because her profit comfortably exceeds the £6,845 Small Profits Threshold, she is treated as having paid Class 2 and pays nothing extra for it while still building her State Pension. Her total deductions are around £8,432, leaving net income of approximately £36,568. If she paid £5,000 into a personal pension, she would cut both her income tax and her Class 4 NI on that slice, illustrating why pension contributions are so tax-efficient for the self-employed.

The self-employed NI burden is markedly lighter than for employees. An employee on £45,000 pays Class 1 NI of around £2,594, and their employer pays a further £6,000 in employer NI. A self-employed person on £45,000 profit pays just £1,945.80 in Class 4 NI with no employer contribution at all. This lower NI cost is one of the recognised trade-offs of self-employment, balanced against the loss of employee rights such as holiday pay, sick pay, and pension auto-enrolment.

Checking Your National Insurance Record

Because Class 4 NI does not build any State Pension entitlement, the contributions that actually matter for your retirement are your Class 2 credits. It is well worth checking each year that you have been credited correctly, especially in years where your profits hover near the Small Profits Threshold. You can view your complete National Insurance record, see how many qualifying years you have, and get a State Pension forecast through your Personal Tax Account on the GOV.UK Check your National Insurance record service. You need 35 qualifying years for the full new State Pension (£230.25 per week in 2025/26) and at least 10 qualifying years to receive any State Pension at all.

If you find gaps, for example from a year when your profits were below £6,845 and you did not pay voluntary Class 2, you may be able to fill them. Self-employed people can usually pay voluntary Class 2 at the lower weekly rate rather than the more expensive Class 3, making it an affordable way to protect a qualifying year. You can normally fill gaps going back up to six years. Always check the figures against your own circumstances or speak to a qualified accountant before paying, as voluntary contributions are not always worthwhile if you are already on track for the full pension.