UK Self Assessment Tax Calculator 2025/26
Calculate your Self Assessment tax bill including income tax, Class 2 and Class 4 NI for self-employed income. Includes Payments on Account estimate.
£
Total business income (turnover) £
Office, travel, materials, etc. £
£
Common profits:
£0
Total Tax Bill
£0
Income Tax
£0
Class 2 NI
£0
Class 4 NI
Self Assessment Breakdown
Payments on Account Estimate
How to Use This Self Assessment Calculator
Enter your total self-employment income (your turnover — all money received from clients), then enter your allowable business expenses. The profit (income minus expenses) is what gets taxed. Add any other income (e.g. from a part-time PAYE job) and any tax already paid at source to see your net bill.
The Formula
Trading Profit = Self-Employment Income − Allowable Expenses
Total Income = Trading Profit + Other Income
Class 2 NI = £3.45 × 52 weeks (if profit > £12,570)
Class 4 NI = 9% on profit £12,570–£50,270 + 2% above
Income Tax = progressive rates on (Total Income − Personal Allowance)
Tax Due = Income Tax + Class 2 + Class 4 − Tax Already Paid
Total Income = Trading Profit + Other Income
Class 2 NI = £3.45 × 52 weeks (if profit > £12,570)
Class 4 NI = 9% on profit £12,570–£50,270 + 2% above
Income Tax = progressive rates on (Total Income − Personal Allowance)
Tax Due = Income Tax + Class 2 + Class 4 − Tax Already Paid
Example
Sophie, freelance designer, £50,000 income, £10,000 expenses:
Trading profit: £50,000 − £10,000 = £40,000
Class 2 NI: £3.45 × 52 = £179
Class 4 NI: (£40,000 − £12,570) × 9% = £2,469
Income tax: (£40,000 − £12,570) × 20% = £5,486
Total tax bill: £179 + £2,469 + £5,486 = £8,134
Payments on Account: £4,067 due 31 Jan + £4,067 due 31 Jul
Trading profit: £50,000 − £10,000 = £40,000
Class 2 NI: £3.45 × 52 = £179
Class 4 NI: (£40,000 − £12,570) × 9% = £2,469
Income tax: (£40,000 − £12,570) × 20% = £5,486
Total tax bill: £179 + £2,469 + £5,486 = £8,134
Payments on Account: £4,067 due 31 Jan + £4,067 due 31 Jul
Extended
Self Assessment Planner
Payment schedule, expense optimisation and quarterly saving targets
Key Self Assessment dates and amounts to prepare for.
| Date | Payment | Amount |
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How much to set aside each month to cover your tax bill.
Frequently Asked Questions
Who needs to file a Self Assessment tax return?
You must file if: you are self-employed with income over £1,000, you earned over £100,000, you have untaxed income over £2,500 (rental, savings, dividends), you are a company director, you have foreign income, you claimed child benefit while earning above £60,000, or HMRC has asked you to file. Deadline: online returns by 31 January following the tax year.
What is Class 2 and Class 4 National Insurance for the self-employed?
For 2025/26: Class 2 NI is £3.45/week (£179.40/year) if your profits exceed £12,570. Class 4 NI is 9% on profits between £12,570 and £50,270, and 2% on profits above £50,270. Both are paid through Self Assessment. Class 2 contributions protect your entitlement to state benefits and the State Pension.
What expenses can I deduct as a self-employed person?
Allowable expenses include: office costs (rent, bills, stationery), travel (mileage at 45p/mile for first 10,000 miles), clothing (uniform or protective clothing only), financial costs (bank charges, insurance), costs of goods sold, marketing and advertising, training courses, professional subscriptions. Personal expenses are never deductible. Keep records for at least 5 years.
What are Payments on Account?
If your Self Assessment tax bill exceeds £1,000 and less than 80% is collected at source, HMRC requires Payments on Account. You pay two instalments: 50% of last year's bill by 31 January and 50% by 31 July. This is an advance payment towards the current year's bill. A balancing payment (or refund) is made by the following 31 January.
How does the Trading Allowance work?
The Trading Allowance of £1,000 means you do not need to report or pay tax on self-employment income below £1,000/year. If your trading income is between £1,000 and your expenses, you can choose to use the allowance instead of claiming actual expenses — whichever gives the better tax result. Above £1,000, you must register for Self Assessment.