Definition
Self Assessment is the system HM Revenue and Customs (HMRC) uses to collect Income Tax that is not taken automatically, for example through PAYE. Sole traders earning over £1,000, landlords and many company directors who receive dividends file a Self Assessment tax return (form SA100) each year. The online return and any tax owed are due by 31 January after the tax year ends.
Dates for the 2025/26 tax year
- 5 October 2026: register if you need to file for the first time
- 31 October 2026: paper return deadline
- 31 January 2027: online return, balance of tax owed and any first payment on account for 2026/27
- 31 July 2027: second payment on account
Missing the online deadline normally brings an initial £100 penalty, and late payment adds interest at the Bank of England base rate plus 4%.
Changes from April 2026
From 6 April 2026, sole traders and landlords with qualifying income over £50,000 are in MTD for Income Tax, which adds quarterly updates through software. Everyone else keeps filing one annual return.
The checklist on who needs to file Self Assessment covers each situation, and SmartFiling’s Self Assessment tax return service starts from £149.
Related questions
- Do company directors need to file a Self Assessment tax return? Not automatically. A return is usually needed for untaxed income, such as dividends above your allowances or rental income, or if HMRC sends a notice to file.
- How do I get an SA302 for a mortgage? Print it from your HMRC online account at least 72 hours after filing.
Related terms
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Payments on account
Payments on account are two advance payments towards your next Self Assessment tax bill, due by 31 January and 31 July.
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SA302
An SA302 is HMRC's tax calculation for a single tax year, showing the income declared on a Self Assessment return and the Income Tax worked out on it.
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Unique Taxpayer Reference (UTR)
A Unique Taxpayer Reference (UTR) is the 10-digit number HM Revenue and Customs (HMRC) gives each taxpayer.
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MTD for Income Tax
MTD for Income Tax (Making Tax Digital for Income Tax) requires sole traders and landlords with qualifying income above a threshold to keep digital records…
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Dividend allowance
The dividend allowance is the amount of dividend income an individual can receive each tax year without paying dividend tax. For 2026/27 it is £500.
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