Glossary · Tax
Self Assessment
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Definition: HMRC's system for collecting Income Tax from people whose tax cannot be fully collected through PAYE — including the self-employed, landlords, and high earners.
Register by 5 October after the tax year you become liable. Online filing deadline is 31 January; paper deadline is 31 October. Payments on account may be due in two instalments (31 January and 31 July).
Primary source: gov.uk/self-assessment-tax-returns