Tax Year Calendar

Why 6 April?

The UK tax year runs from 6 April to 5 April. Not January to December. Not April to March on neat boundaries. 6 April.

This dates back to 1752 when Britain switched from the Julian to the Gregorian calendar, losing 11 days in September. The Treasury refused to lose 11 days of tax revenue, so they shifted the tax year end from 25 March (the old New Year) forward by 11 days to 5 April. The tax year start became 6 April, and nobody's changed it since.

It's quirky. It's confusing for anyone used to calendar years. But once you know the key dates, it becomes straightforward.

The dates that matter

There are really only a handful of dates you need to remember as an employed person. These expand significantly once you become self-employed (covered in Part 2), but for now:

Date	What happens	Who it affects
6 April	New tax year starts. New allowances, new bands, new rates begin.	Everyone
5 April	Tax year ends. Last day to use this year's ISA allowance, pension allowance, and other tax-year-based limits.	Everyone
31 May	Employers must give you your P60 for the year just ended.	Employed people
6 July	Employers must give you a P11D if you received taxable benefits (company car, health insurance, etc.).	Employed people with benefits
31 July	Second payment on account due for Self Assessment.	Self-employed / SA filers
5 October	Deadline to register for Self Assessment if you became self-employed during the previous tax year.	Newly self-employed
31 October	Paper Self Assessment return deadline.	SA filers using paper
31 January	Online Self Assessment deadline AND first payment on account due AND balancing payment for the previous year. The busiest date in the UK tax calendar.	Self-employed / SA filers

Diagram: Tax Year Timeline

Your P60

Your P60 is a summary of your total pay and deductions for the tax year. Your employer must give you one by 31 May after the tax year ends. It shows:

• Total pay for the year
• Total tax deducted
• Total NI deducted
• Your tax code
• Your employer's PAYE reference

Keep your P60. You might need it for mortgage applications, Self Assessment (if you have other income), or checking your State Pension record. If you lose it, your employer can give you a replacement, but they're not legally required to.

Jargon Buster: P60 An annual certificate from your employer showing your total pay and deductions for the tax year. The "P" stands for the PAYE system. You get one for each employment you held during the year.

Your P11D

If you receive benefits in kind from your employer -- a company car, private health insurance, gym membership, interest-free loans over 10,000 -- these are taxable. Your employer reports them to HMRC on a P11D form and must give you a copy by 6 July.

The value of these benefits gets added to your income for tax purposes. HMRC usually adjusts your tax code so the extra tax is spread across the following year's payslips, rather than demanding a lump sum.

If you don't receive any benefits beyond your salary and pension, you won't get a P11D.

Jargon Buster: Benefits in kind (BIK) Non-cash benefits you receive from your employer that have a monetary value. They're taxed as if they were additional salary. Common examples: company car, private medical insurance, interest-free season ticket loans over 10,000.

Your Personal Tax Account

HMRC has an online portal called your Personal Tax Account where you can:

• Check your tax code is correct
• See your estimated income and tax for the current year
• View your State Pension forecast
• Check your National Insurance record
• See if you owe tax or are owed a refund
• Update your address and personal details

You can access it at gov.uk/personal-tax-account. You'll need a Government Gateway account to log in. If you don't have one, the registration takes about 10 minutes.

This is worth checking at least once a year, especially after:

• Starting a new job
• Getting a pay rise
• Receiving a tax code change letter
• The end of the tax year

5 April: Use it or lose it

Several financial allowances reset on 5 April. They don't roll over to the next year. The main ones:

Allowance	Annual limit	What happens if you don't use it
ISA allowance	20,000	Lost. You can't put 40,000 in next year to catch up.
Pension Annual Allowance	60,000	Can carry forward up to 3 years of unused allowance (but you must have been in a pension scheme).
Capital Gains Tax allowance	3,000	Lost. Can't carry forward.
Trading Allowance	1,000	Resets. Not carry-forward.
Dividend Allowance	500	Lost. Down from 1,000 in 2023/24 and 2,000 in 2022/23.

For most employed people, the ISA allowance is the big one. If you have savings, putting them inside an ISA before 5 April ensures future interest is tax-free.

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Real Scenario: Sam and Steve's tax year

Sam's year (employed + side hustle):

Date	What happens for Sam
6 April 2025	New tax year. Sam's Unbought sales crossed 1,000 during the previous year, so Sam needs to register for Self Assessment.
5 October 2025	Deadline for Sam to register with HMRC for Self Assessment (for the 2024/25 tax year). Sam registers online and receives a UTR (Unique Taxpayer Reference) by post.
5 April 2026	Tax year ends. Sam puts 2,000 into a Cash ISA before the deadline.
31 January 2027	Sam files the 2025/26 Self Assessment return online and pays any tax owed.

Sam's employed income is handled automatically through PAYE. But the Unbought income isn't -- that needs Self Assessment. Sam will learn exactly how in Chapter 8.

Steve's year (employed, considering going solo):

Date	What happens for Steve
6 April 2025	New tax year. Steve is still employed but doing weekend gardening jobs. His side income is under 1,000 so the Trading Allowance covers it -- no need to register yet.
31 May 2025	Steve gets his P60 from the landscaping company. Gross pay: 28,000. Tax paid: 3,086.
Throughout 2025	Steve's weekend gardening business grows. By autumn, he's earning 200/month from it regularly.
5 April 2026	Tax year ends. Steve's side income hit 2,400 for the year -- above the 1,000 Trading Allowance. He'll need to register for Self Assessment.
5 October 2026	Steve registers as self-employed with HMRC.

Key point: The Trading Allowance of 1,000 means if your self-employed income is below this amount, you don't need to tell HMRC or file a return. But the moment you cross it, even by a pound, you need to register by the following 5 October.

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Checklist: End of tax year

• Check your tax code is correct via your Personal Tax Account
• Use your ISA allowance before 5 April (20,000 max)
• Check if you've earned more than 1,000 from any side income (Trading Allowance threshold)
• Keep your P60 when it arrives by 31 May
• Check your P11D if you receive employee benefits (by 6 July)
• Review your State Pension forecast (gov.uk/check-state-pension)

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Jargon Buster

Term	Plain English
Tax year	The 12-month period from 6 April to 5 April that HMRC uses for calculating your tax
P60	Annual summary from your employer showing your total pay and deductions for the tax year
P11D	Form listing taxable benefits you received from your employer (company car, health insurance, etc.)
Self Assessment	The process of filing your own tax return with HMRC, required if you have income not covered by PAYE
UTR	Unique Taxpayer Reference -- a 10-digit number HMRC gives you when you register for Self Assessment
Trading Allowance	1,000 of self-employed or miscellaneous income that's tax-free without needing to report it
Personal Tax Account	Your online HMRC account where you can check your tax code, pension forecast, and NI record
Payment on Account	An advance payment towards next year's tax bill, based on the previous year's liability. Due 31 January and 31 July
Government Gateway	The login system for HMRC online services