What is Tax Year?
The UK tax year runs from 6 April to 5 April the following year. All income, expenses, and tax calculations for self-assessment are based on this 12-month period.
The UK tax year (also called the fiscal year for individuals) runs from 6 April to 5 April the following year. For example, the 2025/26 tax year runs from 6 April 2025 to 5 April 2026.
This period determines:
- Which income and expenses count towards your self-assessment tax return
- Your personal allowance and tax band thresholds
- Your National Insurance contributions
- Filing and payment deadlines
Key dates within and after each tax year:
- 6 April: New tax year begins — new allowances and rates take effect
- 5 April: Tax year ends — finalise your income and expense records
- 31 July: Second payment on account due (based on previous year's tax bill)
- 5 October: Deadline to register for self-assessment if newly self-employed
- 31 January: Online filing deadline and first payment on account due
The unusual 6 April start date has historical origins dating back to 1752 when Britain adopted the Gregorian calendar. While it may seem odd, it is firmly established and unlikely to change.
As a freelancer, it is essential to track your income and expenses by tax year. Keep a running total throughout the year so you are not scrambling at year-end. Invoicing software that tags transactions by tax year makes this much easier.
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Frequently Asked Questions
Why does the UK tax year start on 6 April?
The 6 April start date dates back to 1752 when Britain adopted the Gregorian calendar and lost 11 days. The Treasury refused to lose 11 days of tax revenue, so the tax year was extended from 25 March (the old new year) to 5 April. It has remained ever since.
Which tax year does my invoice belong to?
An invoice generally belongs to the tax year in which the income was earned or received, depending on your accounting method. Most sole traders use the cash basis, meaning it falls in the tax year when the payment hits your bank account.
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