The Complete Guide to Self Assessment 2025
Self Assessment can be daunting, but understanding the deadlines and requirements is half the battle. Here is everything you need to know about filing your tax return this year.
Do I need to file a tax return?
You must send a tax return if, in the last tax year (6 April to 5 April), you were:
- Self-employed as a 'sole trader' and earned more than £1,000 (before taking off anything you claimed tax relief on).
- A partner in a business partnership.
- Earning £100,000 or more (though this threshold has been changing, always check current HMRC guidance).
- Earning income from untaxed savings, investments, or dividends.
- Earning income from renting out a property.
Key Deadlines
- 5 October 2025: Deadline to register for Self Assessment if you're new.
- 31 October 2025: Deadline for paper tax returns.
- 31 January 2026: Deadline for online tax returns.
- 31 January 2026: Deadline for paying the tax you owe.
Penalties for Late Filing
HMRC is strict with deadlines. You’ll get a £100 penalty if your tax return is up to 3 months late. You’ll have to pay more if it’s later, or if you pay your tax bill late. You’ll also be charged interest on late payments.
What you need to file
Before you start, gather your records:
- Your UTR (Unique Taxpayer Reference) number.
- Your National Insurance number.
- Records of expenses related to your self-employment.
- P60 form from your employer (if you also have a salary).
- P11D form for benefits and expenses.
- Certificates for interest from banks and building societies.
Payments on Account
If your tax bill is more than £1,000, you may have to make 'payments on account'. These are advance payments towards your next tax bill. You make two payments a year: one by 31 January and one by 31 July.
Disclaimer: This guide is for informational purposes only. Tax laws can change, and you should consult a professional accountant or HMRC for advice specific to your situation.