Self Assessment: what to do and when

Self Assessment is how HMRC collects Income Tax that isn't taken automatically, for example through PAYE on a salary. Once a year you send a tax return for the tax year that runs from 6 April to 5 April, and pay what you owe.

Who needs to send one

• You're self-employed as a sole trader and earned more than £1,000 (before expenses) in the tax year.
• You're a partner in a business partnership.
• You have income that hasn't been taxed, such as rent from a property or dividends from your own company.

There are other reasons too. If you're not sure, use HMRC's checker (opens in new tab).

The dates

• 5 October: register for Self Assessment if it's your first time, for the tax year that ended the April before. Register on GOV.UK (opens in new tab).
• 31 October: the deadline for a paper return.
• 31 January: the deadline for an online return, and to pay what you owe for the last tax year. If you make payments on account, the first one for the current year is due the same day.
• 31 July: your second payment on account, if you make them.

For example, for the 2025/26 tax year (6 April 2025 to 5 April 2026), the online return and the payment are due by 31 January 2027.

What to do, step by step

1. 1Through the year, keep records of your income and expenses. Keep them for at least 5 years after the 31 January deadline.
2. 2After 5 April, gather your figures: sales, allowable expenses, rent, interest, dividends and any pension contributions.
3. 3Sign in to your HMRC online account and fill in the return, or use software or an accountant.
4. 4The online return works out your bill. Note the amount and when it's due.
5. 5Pay by 31 January. See ways to pay on GOV.UK (opens in new tab).

If you're late

• Sending your return late: a £100 penalty straight away, even if you owe no tax. After 3 months, £10 a day for up to 90 days, and more after 6 and 12 months.
• Paying late: interest from the day after the deadline, and late payment penalties that grow the longer the tax is unpaid.

See Self Assessment penalties on GOV.UK (opens in new tab). If you can't pay in full, contact HMRC before the deadline: you may be able to set up a payment plan.

Octotax shows your Self Assessment dates on your octagon and emails you before each one. Track your deadlines, free. General information, not tax advice.