HMRC Self Assessment 2026: complete guide for freelancers and sole traders
Filing your Self Assessment tax return for the first time can feel overwhelming. This guide breaks down exactly what HMRC needs, what deadlines matter, and how to calculate your tax bill — step by step.
What is Self Assessment?
Self Assessment is HMRC's system for collecting Income Tax and National Insurance from people who are self-employed, earn income from multiple sources, or have complex tax affairs. As a sole trader or freelancer, you must file a Self Assessment return every year to declare your income and pay the right amount of tax.
Key deadlines for 2025/26 tax year
| Deadline | Action required |
|---|---|
| 5 April 2026 | End of 2025/26 tax year |
| 5 October 2026 | Register for Self Assessment if not already registered |
| 31 October 2026 | Deadline for paper tax returns |
| 31 January 2027 | Deadline for online tax return AND payment of tax owed |
| 31 July 2027 | Second payment on account (if applicable) |
What income to declare
- All self-employment income (including cash payments — HMRC can check bank statements)
- Rental income from property
- Dividends from company shares
- Income from savings and investments above the savings allowance
- Foreign income if you are UK resident
- Capital gains from selling assets (property, shares, crypto)
How to calculate your tax bill
The basic calculation: Total income minus allowable expenses = Net profit. Net profit minus Personal Allowance (£12,570 in 2025/26) = Taxable income. Apply income tax rates: 20% basic rate on £12,571-£50,270; 40% higher rate on £50,271-£125,140; 45% additional rate above £125,140. Add Class 4 National Insurance contributions on top.
Payments on account
If your tax bill is over £1,000, HMRC requires you to make two advance payments towards next year's tax bill — called "payments on account". Each payment is 50% of the previous year's tax bill. The first is due 31 January, the second 31 July. First-time Self Assessment filers often get a shock at their first January payment — budget for this.
How to file online
- Log in to your Government Gateway account at gov.uk/log-in-file-self-assessment
- Enter your UTR and password
- Complete the Self Employment section with your income and expenses
- Review the tax calculation HMRC generates
- Pay any tax owed by 31 January
Penalties for late filing
- 1 day late: £100 automatic penalty
- 3 months late: £10 per day (maximum £900)
- 6 months late: 5% of tax owed or £300 (whichever is greater)
- 12 months late: further 5% of tax owed or £300