Self Assessment is the way HMRC collects Income Tax from people whose tax is not fully taken at source through PAYE — the self-employed, landlords, some company directors, and anyone with substantial untaxed income. These guides explain who needs to file, the deadlines that matter, how payments on account work and how to avoid penalties.
Tax rules, rates and thresholds change from one tax year to the next and depend on your personal circumstances, so always confirm current figures on GOV.UK or with HMRC before you act.