The tax year is the 12 months from 6 April to the following 5 April, used for Income Tax, National Insurance and Self Assessment. It is written with both years, for example 2026 to 2027.
What it is used for
Income Tax rates and allowances are set for each tax year, and a Self Assessment return reports the income of one tax year. The year from 6 April 2026 to 5 April 2027 is the 2026 to 2027 tax year, and its return and tax are due by 31 January 2028.
Sole traders and landlords
A sole trader is taxed on the profit of the tax year itself, whatever date their accounts are made up to. Accounts made up to 31 March are treated as if they ran to 5 April, which is why most sole traders use a 31 March or 5 April year end. Under Making Tax Digital for Income Tax, the quarterly updates follow the tax year too.
Companies are different
A company is not taxed by tax year. It pays Corporation Tax for its own accounting period, and Corporation Tax rates are set for the financial year, which runs from 1 April to 31 March.
Read more: Self Assessment in Tax Optimiser.