Self Assessment Tax Returns
Written in plain language for general understanding. This is educational content, not legal advice. Based on UK Acts of Parliament, statutory instruments, and official guidance.
UK National Law
What is this right?
If you're self-employed, a company director, or have significant untaxed income, you'll need to file a Self Assessment tax return each year.
Key annual deadlines:
- 5 October: Register for Self Assessment if you're new
- 31 October: Paper return deadline
- 31 January: Online return deadline and payment of tax due
- 31 July: Second payment on account (advance payment toward next year's tax)
Penalties for late filing: £100 immediately, then additional penalties after 3 months, 6 months, and 12 months. Late payment incurs interest plus 5% surcharges at 30 days, 6 months, and 12 months.
When does it apply?
- You are self-employed and earned more than £1,000 in a tax year.
- You are a company director (unless of a non-profit).
- You have untaxed income — rental income, foreign income, savings/investment income above your allowance, or capital gains.
- You earned over £150,000 (since reduced to £100,000 for some requirements).
- You need to claim tax relief on pension contributions, charitable donations, or employment expenses over £2,500.
What should you do?
- Register early — HMRC can take weeks to set up your account and post your Unique Taxpayer Reference (UTR).
- Keep records of all income and expenses — you must keep them for at least 5 years after the 31 January deadline.
- File your return online through HMRC's Self Assessment service — it calculates your tax automatically.
- If you can't pay in full, contact HMRC to set up a Time to Pay arrangement — they may agree to monthly instalments.
- Consider using HMRC-recognised software or an accountant if your affairs are complex.
What should you NOT do?
- Don't miss the 31 January deadline — even if you owe nothing, a late return means a £100 penalty.
- Don't guess your figures — use actual records. HMRC can charge penalties for inaccurate returns.
- Don't ignore HMRC letters — failing to respond can escalate penalties and trigger an investigation.
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