Self Assessment is the system HMRC uses to collect Income Tax from people whose tax is not all deducted at source, such as the self-employed, landlords and partners. They report their income on a tax return after the tax year ends.
Who needs to file
Most employees pay their tax through PAYE and never file a return. You normally need to register for Self Assessment if you are self-employed with trading income of more than £1,000, a partner in a partnership, a landlord, or you have other untaxed income or capital gains to report.
Key dates
The tax year runs from 6 April to 5 April.
| Date | What is due |
|---|---|
| 5 October | Register, if you have not filed before |
| 31 October | Paper returns |
| 31 January | Online returns, and payment of the tax you owe |
| 31 July | Second payment on account |
A return filed up to three months late carries a £100 penalty, with more for longer delays.
Making Tax Digital
From 6 April 2026, sole traders and landlords with qualifying income over £50,000 move to Making Tax Digital for Income Tax, which replaces the annual return with quarterly updates and a final declaration.
Read more: Self Assessment in Tax Optimiser and Getting started with Self Assessment.