How to file your Self Assessment tax return: step by step

The deadline for filing your 2025/26 return online and paying what you owe is 31 January 2027. Here's how to get it done in an evening.

Before you start

Gather these first and the return itself is the easy part:

• Your UTR (Unique Taxpayer Reference), the 10-digit number HMRC sent when you registered
• Your Government Gateway sign-in for your HMRC online account
• Your total self-employed income and expenses for 6 April 2025 to 5 April 2026
• Your P60 if you also had a job, plus any P11D for benefits
• Interest from savings, dividends, rental income and pension contributions you paid yourself

Filling it in

Sign in to your HMRC online account and choose to file your Self Assessment return. The online form only shows the sections that apply to you, based on a few questions at the start.

• Self-employment: enter your turnover and allowable expenses. If your turnover was under £90,000 you can give a single total for expenses.
• Employment: copy pay and tax from your P60.
• Other income: savings interest, dividends, property income.
• Tax reliefs: private pension contributions and Gift Aid donations can lower your bill, so don't skip them.

Before you submit, HMRC shows a tax calculation. Check it against your own estimate. If it's very different, something has usually been entered in the wrong box.

Paying

You can pay by bank transfer, debit card or through the HMRC app. Your payment reference is your UTR followed by the letter K. Allow three working days for a bank transfer to arrive.

If this is your first return and your bill is over £1,000, you'll usually also pay the first payment on account towards next year at the same time.

If you can't pay in full

File on time anyway. Late filing and late payment are penalised separately, so filing on time avoids the first £100 penalty. If you owe £30,000 or less you can usually set up a payment plan online.

Common mistakes

• Forgetting to claim allowable expenses, or the £1,000 trading allowance
• Entering monthly figures instead of the annual total
• Missing the student loan section, which HMRC uses to collect repayments
• Leaving it until 31 January, when the HMRC helpline is busiest

General guidance, not tax advice. Check GOV.UK for the latest rules.