Self Assessment is used to tell HMRC about any income that you might need to pay tax on. For instance, if you’re a sole trader, a partner in a partnership (and for the partnership itself), or the director of a limited company.
Submitting Self Assessment doesn’t always mean you’ll have a bill to pay, and can sometimes result in a tax rebate.
This process is expected to change for some taxpayers in April 2026, with the introduction of MTD Income Tax Self Assessment.