Self Assessment Tax Return: A Simple UK Guide to Deadlines and Penalties
Do you need to file a Self Assessment tax return? Who needs one, the key deadlines including 31 January 2027, and how to avoid penalties.
Every year, millions of people in the UK file a Self Assessment tax return with HMRC. If you're self-employed, have a side income or receive certain other income, you might need to file one too.
This guide explains who needs to file, the key deadlines, and how to avoid penalties. It's a general guide, so always check the details on GOV.UK.
Who needs to file a tax return?
You may need to file a Self Assessment tax return if, in the last tax year (6 April to 5 April), you:
- were self-employed and earned more than £1,000 from it,
- were a partner in a business partnership,
- had rental income or other untaxed income,
- or had other income that wasn't taxed through PAYE.
HMRC's online tool on GOV.UK can tell you if you need to file.
Get our best buying guides
New reviews, price drops and deals we trust, sent straight to your inbox. No spam.
Key deadlines for the 2025 to 2026 tax year
| What | Deadline |
|---|---|
| Register for Self Assessment (if you're new) | 5 October 2026 |
| Paper tax return | Midnight, 31 October 2026 |
| Online tax return | Midnight, 31 January 2027 |
| Pay any tax you owe | 31 January 2027 |
Penalties for missing the deadline
If your return is late, there's usually an automatic £100 penalty, even if you don't owe any tax. Further penalties and interest are added if it's later still, and interest is charged on tax paid late. So it's worth filing early.
Tips to make it easier
- Keep records all year. Save invoices, receipts and bank statements in one folder as you go.
- Use a separate bank account for your business or side income.
- Claim allowable expenses, such as some costs of running your business.
- File early. You don't have to pay until 31 January, but filing early tells you what you owe in good time.
- Set money aside for your tax bill each month.
- Watch out for scams. HMRC won't ask for bank details by text or email. If in doubt, contact HMRC directly.
Making Tax Digital
HMRC is moving Self Assessment to Making Tax Digital. From April 2026, many self-employed people and landlords with qualifying income over £50,000 must keep digital records and send quarterly updates using compatible software, with lower income thresholds following in later years. Check GOV.UK to see if this applies to you.
Common questions
When is the Self Assessment deadline?
For the 2025 to 2026 tax year, the online deadline is midnight on 31 January 2027. Paper returns were due by 31 October 2026.
What happens if I file late?
You'll usually get an automatic £100 penalty, with more penalties and interest if it's very late or tax is paid late.
Do I need to file if I earn under £1,000 from a side hustle?
Usually not, because of the £1,000 trading allowance, unless you need to file for another reason. See our side hustle guide.
Should I use an accountant?
Many people file on their own. An accountant can help if your finances are complex, or if you'd like peace of mind.
Related guides
This guide is for general information only and is not tax advice. Tax rules can change, so always check GOV.UK or speak to a qualified accountant.
Savified publishes independent buying guides for UK shoppers. We research products, compare them across trusted UK retailers and keep prices up to date, so you can buy with confidence.
About Savified →
