Paying NI Through Self Assessment

Key facts

Class 2 and Class 4 NI are calculated automatically when you file your Self Assessment return.
They are added to your Income Tax liability to form your total tax bill, due 31 January.
Class 4 NI is included in your payments on account (31 January and 31 July).
Under MTD for Income Tax, NI will be calculated as part of the final declaration.

NI and Self Assessment

If you are self-employed, your National Insurance contributions are not deducted from a salary each month (like an employee’s Class 1 NI). Instead, they are calculated and collected through the Self Assessment system — the same process you use to report your income and pay Income Tax.^[1]

What Gets Calculated

When you file your Self Assessment tax return, HMRC calculates two types of NI:^[3]

NI Class	How It’s Calculated	2026/27 Rate
Class 2	Flat rate × number of weeks self-employed	£3.65/week (£189.80/year)
Class 4	Percentage of self-employment profits	6% (£12,570–£50,270); 2% above

How NI Appears on Your Tax Bill

Your Self Assessment tax bill (known officially as the “Statement of Account”) shows your total liability broken down into:^[2]

Income Tax — calculated on your total taxable income from all sources
Class 2 NI — shown as a separate line item
Class 4 NI — shown as a separate line item
Student loan repayments (if applicable)
Less: Payments on account already made
Balancing payment due

Example tax bill for £35,000 self-employment profit (2026/27):

Income Tax: £4,486.00 (20% on £22,430 above personal allowance)
Class 4 NI: £1,345.80 (6% on £22,430 above Lower Profits Limit)
Class 2 NI: £189.80
Total liability: £6,021.60

Payments on Account

If your Self Assessment bill is more than £1,000 (and less than 80% was collected at source through PAYE), you must make payments on account:^[2]

Payment	Due Date	Amount
First payment on account	31 January (during the tax year)	50% of previous year’s total bill
Second payment on account	31 July (after the tax year)	50% of previous year’s total bill
Balancing payment	31 January (after the tax year)	Remainder after payments on account

Important: Class 4 NI is included in payments on account, but Class 2 NI is not. Class 2 is added to your balancing payment on 31 January. This catches some people out — your January bill may be slightly higher than half your total liability.

The Filing Process

When you complete your Self Assessment tax return:^[1]

Report your self-employment income and expenses on the self-employment pages (SA103S for short or SA103F for full)
Your net profit is calculated
HMRC’s system automatically calculates your Class 4 NI based on this profit figure
Class 2 NI is added based on the number of weeks you were self-employed during the year
If your profits are below the Small Profits Threshold (£7,105), you can opt in to voluntary Class 2
The total (Income Tax + Class 2 + Class 4) forms your tax bill

MTD for Income Tax: How NI Will Work

When Making Tax Digital for Income Tax takes effect, the Self Assessment tax return will be replaced by digital quarterly updates and a final declaration:^[4]

Quarterly updates: You submit income and expense summaries every quarter. No NI is calculated at this stage
End of period statement: You confirm each business source’s figures for the year
Final declaration: This replaces the tax return. HMRC calculates your total liability including Income Tax, Class 2 NI, and Class 4 NI

The fundamental NI calculations will remain the same — the change is in how you report the underlying income and expenses.

Common Situations

First year of self-employment

In your first year, you won’t have previous payments on account. Your first bill is due on 31 January following the end of the tax year, plus a first payment on account for the next year. This means your first January bill can feel like a “double payment.”

Closing your business

If you stop being self-employed during the tax year, Class 2 NI is charged only for the weeks you were self-employed. Class 4 is calculated on the profits earned during the period of self-employment.

Losses

If your self-employment results in a loss, there is no Class 4 NI to pay (since there are no profits). Class 2 is still due unless your profits are below the Small Profits Threshold — a loss is below the threshold, so Class 2 becomes voluntary.

Key Deadlines

Deadline	What It’s For
5 October	Register for Self Assessment with HMRC (if newly self-employed)
31 October	Paper tax return filing deadline
31 January	Online filing deadline + payment of balancing payment + first payment on account
31 July	Second payment on account

Frequently Asked Questions

Do I pay NI separately from my tax?

No. For self-employed people, Class 2 and Class 4 NI are included in your Self Assessment tax bill. You pay them at the same time as your Income Tax — in one combined payment. There is no separate NI invoice.

Is NI included in my payments on account?

Class 4 NI is included in payments on account. Class 2 NI is not included in payments on account — it is added as a separate amount to your 31 January balancing payment. This means your January bill may be slightly higher than expected.

How will NI work under MTD for Income Tax?

Under Making Tax Digital, you will submit quarterly updates of income and expenses, but NI will not be calculated until the final declaration (replacing the Self Assessment tax return). Class 2 and Class 4 will be calculated at that point and included in your final bill.

What if I cannot afford to pay my NI bill?

Since NI is part of your Self Assessment bill, you can apply for a Time to Pay arrangement with HMRC if you cannot pay in full by the deadline. Call the Self Assessment payment helpline on 0300 200 3822 to discuss options. Interest will be charged on late payments.

Sources

Self Assessment tax returns — GOV.UK
Understand your Self Assessment tax bill — GOV.UK
Self-employed National Insurance rates — GOV.UK
Making Tax Digital for Income Tax — GOV.UK