Self Assessment for beginners: how to file your first tax return (31 January 2027)

Do you need to file a tax return?

You usually need to file Self Assessment if, in the tax year, you:

• Earned more than £1,000 from self-employment or a side hustle (rising to £3,000 from the 2027/28 tax year)
• Received more than £1,000 from property, or more than £7,500 from a lodger under the Rent a Room scheme
• Had other untaxed income HMRC has asked you to report

If you are not sure, HMRC has a free check if you need to send a tax return tool.

Step 1: register

If it is your first return, register for Self Assessment on GOV.UK. The deadline is 5 October after the end of the tax year you first need to report, so 5 October 2026 for 2025/26.

You will get a Unique Taxpayer Reference (UTR) by post, which can take up to 15 working days. If you have missed 5 October, register now anyway: the sooner you do, the better.

Step 2: gather what you need

• Your UTR and Government Gateway login
• Your National Insurance number
• Your P60 or P45 from any job, showing pay and tax already paid
• Your side hustle income and expenses for the tax year
• Rental income and costs, if you have them
• Bank interest, if it is over your Personal Savings Allowance
• Pension contributions and Gift Aid donations, which can reduce your bill

Step 3: fill in the return

1. Sign in to your HMRC online account.
2. Answer the questions about what income you had. The return only shows the sections you need.
3. For self-employment, enter your total income and either your expenses or the trading allowance.
4. Check the tax calculation HMRC shows you before you submit.
5. Submit and save the confirmation.

Free toolSide hustle tax calculatorSee how much tax and National Insurance you owe on side income, and what to set aside each month.→

Step 4: pay what you owe

Pay by 31 January 2027 for the 2025/26 tax year. You can pay by bank transfer, debit card or through the HMRC app. If your job's tax code can collect it, HMRC may take bills under £3,000 through your salary instead, as long as you file online by 30 December.

If your bill is over £1,000, you may also have to make payments on account towards next year. In your first year that can mean paying about one and a half times your bill in January.

Deadlines and penalties

If you file late:

• 1 day late: £100 fixed penalty
• 3 months late: £10 a day, up to £900
• 6 months late: a further 5% of the tax due or £300, whichever is more
• 12 months late: another 5% or £300

Paying late adds interest from the day after the deadline, and further penalties of 5% of the unpaid tax at 30 days, 6 months and 12 months.

Cannot pay in full?

File on time anyway, then set up a Time to Pay plan online if you owe less than £30,000. Filing on time avoids the late filing penalties even if you need longer to pay.

Free toolMaking Tax Digital checkerFind out if and when you need MTD software and quarterly updates for your side income or rent.→

Common questions

When is the Self Assessment deadline?

31 January 2027 for online returns covering the 2025/26 tax year. Paper returns were due by 31 October 2026.

How long does it take to do a tax return?

For a simple side hustle with tidy records, often under an hour. Most of the time goes into finding your figures, so keep records through the year.

Do I need an accountant for Self Assessment?

Not for a simple side hustle. An accountant can help if you have several income sources, property, or a large bill to plan for.