Tax Year
The 12-month period used for UK tax purposes, running from 6 April to the following 5 April. All income tax, National Insurance, and Capital Gains Tax calculations are based on the tax year, not the calendar year. The unusual start and end dates derive from an 18th-century change to the calendar that the Exchequer declined to adopt for tax purposes.
How it works
Every income tax, National Insurance, and Capital Gains Tax calculation is anchored to the tax year in which the income or gain arose, not the calendar year in which you file a return or receive a payslip. A bonus paid on 10 April, for example, falls into the new tax year even though it might relate to performance in the previous calendar year.
Key deadlines are set relative to the tax year rather than the calendar year: Self Assessment returns for a tax year are due online by 31 January following its end, and employers must issue P60 certificates summarising the year's pay and tax by 31 May. Tax codes, allowances, and thresholds are also set for a specific tax year and can change from one year to the next, which is why the same salary can produce a different tax bill in consecutive years.
The odd 6 April start date is a historical artefact: when Britain adopted the Gregorian calendar in 1752, eleven days were dropped to align with the rest of Europe, but the Treasury moved the tax year's start date to preserve a full year of revenue rather than losing eleven days of collection. The date has stuck ever since, even though almost no other UK administrative process still uses it.
Frequently asked questions
Why doesn't the UK tax year run from January to December like most other countries?
It's a historical accident dating to the 1752 calendar reform — the Treasury shifted the start date to avoid losing eleven days of tax revenue when Britain adopted the Gregorian calendar, and the resulting 6 April start has simply never been changed.
Which tax year does a bonus paid in early April fall into?
Whichever tax year contains the actual payment date, not the period the bonus relates to — a bonus paid on 6 April or later falls into the new tax year even if it was earned largely during the previous one.
How is a tax year written out, like 2026-27?
It's written as the two calendar years it spans, so the 2026-27 tax year runs from 6 April 2026 to 5 April 2027, and you'll see this format used throughout HMRC guidance, payslips, and tax software.
Related Terms
HMRC
His Majesty's Revenue and Customs, the UK government department responsible for collecting taxes, paying certain forms of state support, and enforcing tax law.
Self Assessment
The system by which individuals report their own income, gains, and reliefs to HMRC each year through an online or paper tax return, rather than having tax collected automatically under PAYE.
PAYE
Pay As You Earn — the system by which employers deduct income tax and National Insurance directly from employees' wages before paying them, and remit the deductions to HMRC on their behalf.
P60
An annual certificate your employer gives you at the end of the tax year (by 31 May) summarising your total pay and total tax deducted under PAYE for the year.