Self Assessment Tax Bill Calculator UK 2026–27
Estimate your Self Assessment tax bill for 2026–27. Enter your self-employment profit to see income tax, Class 4 National Insurance (6% / 2%), and student loan repayments in one place. Covers all income tax bands including the personal allowance taper above £100,000.
Rates correct for 2026–27 · Reviewed by the Richard Ross · Last updated April 2026
Do I need to file a Self Assessment return?
Answer these questions to find out.
Your estimated SA bill
Total SA bill
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Income tax
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Class 4 NI
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Enter your details above and click “Estimate my SA bill” to see your results.
How Self Assessment tax works for the self-employed
When you are self-employed, you are responsible for calculating and paying your own tax. Unlike employees whose tax is deducted at source via PAYE, self-employed individuals report their income and expenses via an annual Self Assessment tax return and pay the resulting bill directly to HMRC.
Income tax on self-employment profit
Income tax is charged on your taxable profit — the amount remaining after allowable business expenses are deducted from your income. The same income tax rates and bands apply as for employment income: the personal allowance (£12,570 in 2026–27) is deducted first, and the remainder is taxed at 20% (basic rate, up to £50,270), 40% (higher rate, £50,270–£125,140), or 45% (additional rate, above £125,140). The personal allowance tapers for high earners: it reduces by £1 for every £2 of income above £100,000, reaching zero at £125,140.
Worked example: £50,000 self-employment profit
Self Assessment tax bill (2026–27):
- Profit: £50,000
- Personal allowance: £12,570 (tax-free)
- Income tax at 20%: £37,430 × 20% = £7,486
- Class 4 NI at 6%: £37,430 × 6% = £2,245.80
Total tax bill: £9,731.80
Effective rate: 19.5% on £50,000 profit
Plus first payment on account: 50% of £9,731.80 = £4,865.90, due 31 January alongside the main bill. Total January payment: £14,597.70. Use the take-home pay calculator to compare with employment income at the same level.
Class 4 National Insurance
Rather than the employee Class 1 rates, Class 4 NI applies to self-employed profits above the lower profits limit. In 2026–27, Class 4 NI is charged at 6% on profits between £12,570 and £50,270, and 2% on profits above £50,270. Class 4 NI does not count towards your NI record for state pension purposes — Class 2 NI (or voluntary contributions) does that.
Class 2 NI (£3.50/week if profits exceed £12,570) is treated as a voluntary payment from 2024–25 but is still worth paying to protect your state pension entitlement. This calculator does not include Class 2 NI.
Payments on account
HMRC operates a payments on account system for Self Assessment taxpayers with a bill above £1,000. You make two advance payments towards the following year's bill — each equal to 50% of the current year's total. The first payment on account is due by 31 January alongside your tax bill; the second is due 31 July. Any balancing payment (if your actual bill is higher than the payments made) is due 31 January the following year.
In your first year of self-employment, your January bill can therefore be 150% of the year's tax (100% for the year just ended, plus 50% payment on account for the next year). Planning ahead for this is important.
Student loan repayments via Self Assessment
If you have a student loan, repayments are calculated on your total income above the threshold for your plan type. For sole traders, HMRC collects student loan repayments through Self Assessment rather than PAYE. The repayment is included on your Self Assessment return and paid alongside your tax bill.
Contractors and IR35
Contractors who operate through a limited company may need to consider their Self Assessment position alongside their IR35 status. Outside IR35, profits extracted as dividends are not subject to the same Class 4 NI rates as self-employment income, but must still be declared on your Self Assessment return. If you also realised a capital gain during the year, this is reported on the same return.
Sources: HMRC — Self Assessment tax returns (gov.uk), HMRC — Self-employed NI rates (gov.uk)
Frequently asked questions
Who needs to file a Self Assessment tax return?
You must file a Self Assessment return if you were self-employed as a sole trader and earned more than £1,000, if you were a partner in a business partnership, if your income was over £100,000, if you had untaxed income over £2,500 (from renting property, for example), or if you received income from abroad. HMRC also requires returns for those with complex tax affairs, such as those with significant investment income or Child Benefit where income exceeded £60,000. Contractors operating through a limited company may be subject to IR35 rules — use our IR35 Calculator to check.
What is Class 4 National Insurance?
Class 4 NI is the National Insurance paid by self-employed individuals on their profits. It is calculated at 6% on profits between £12,570 and £50,270, and 2% on profits above £50,270. Unlike employed workers who pay Class 1 NI through PAYE, self-employed people pay Class 4 via their Self Assessment return. You may also choose to pay Class 2 NI (£3.50/week) if your profits exceed the Small Profits Threshold of £12,570 — this is voluntary from April 2024 but protects your state pension entitlement.
What are payments on account?
Payments on account are advance payments towards your next year's tax bill. HMRC requires two payments on account — one by 31 January and one by 31 July — each equal to 50% of your previous year's Self Assessment bill. This means in your first year of self-employment you pay your full tax bill by 31 January, plus 50% on account for the following year. If your income is likely to be significantly lower in the following year, you can apply to reduce your payments on account.
What expenses can I deduct from self-employment profit?
You can deduct allowable business expenses before calculating your taxable profit. These include office costs, travel expenses (excluding ordinary commuting), stock and materials, marketing, professional fees, and a proportion of home costs if you work from home. Capital purchases (equipment, vehicles) are claimed via the Annual Investment Allowance rather than as direct expenses. HMRC's simplified expenses scheme offers flat rates for mileage, working from home, and living at your business premises.
How does the personal allowance apply to self-employment income?
The standard personal allowance of £12,570 applies to self-employment profit in the same way as employment income. Profit up to £12,570 is free of income tax. Profit between £12,570 and £50,270 is taxed at 20% (basic rate). Profit between £50,270 and £125,140 is taxed at 40% (higher rate). Above £125,140 the rate is 45%. The personal allowance tapers by £1 for every £2 of income above £100,000.
How much tax do I pay on £40,000 self-employment profit?
On £40,000 profit in 2026-27: income tax is £5,486 (£0 on the first £12,570, then 20% on £27,430). Class 4 NI is £1,645.80 (6% on £27,430). Total tax bill: £7,131.80. Your effective tax rate is 17.8% on the full £40,000. If you also have a student loan, repayments are calculated on top of this.
When is the Self Assessment deadline for 2026-27?
Paper returns must be filed by 31 October 2027. Online returns must be filed by 31 January 2028. The tax you owe must be paid by 31 January 2028, along with the first payment on account for 2027-28. The second payment on account is due 31 July 2028. Late filing triggers an automatic £100 penalty, increasing with further delay.
Can I deduct pension contributions from my Self Assessment profit?
If you contribute to a pension via relief at source, the pension provider claims basic rate relief automatically. You can claim additional higher or additional rate relief through your Self Assessment return. If you use salary sacrifice through a PAYE employer (not applicable to sole traders), the contribution is deducted before tax. Self-employed individuals can also use their profit figure to determine their annual allowance.
Do I pay NI on dividend income declared through Self Assessment?
No. National Insurance is only charged on earned income — employment earnings and self-employment profits. Dividends, savings interest, and rental income are not subject to NI, though they must be declared on your Self Assessment return for income tax purposes. Dividend tax rates (8.75% / 33.75% / 39.35%) apply instead.
What happens if I miss the Self Assessment deadline?
Late filing: £100 penalty immediately, rising to £10 per day after 3 months (up to £900), then further penalties at 6 and 12 months. Late payment: interest accrues from 1 February, plus a 5% surcharge at 30 days, 6 months, and 12 months overdue. If you cannot pay, contact HMRC to arrange a Time to Pay plan — interest still accrues but penalties may be reduced.
Related calculators
This calculator provides estimates only. Results are based on the 2026–27 tax year. Credibrate is not a tax adviser. For personalised advice speak to a qualified accountant.