If you’ve ever found yourself staring at the calendar wondering why the UK tax year doesn’t just start on 1 January like everything else, you’re not alone. The 2023/24 tax year ran from 6 April 2023 to 5 April 2024, and getting these dates right is the difference between a smooth self-assessment and an automatic £100 penalty.

4 related posts

UK tax year start date: 6 April · UK tax year end date: 5 April · Duration: 365 days (366 in leap year) · Current tax year (as of 2025): 2024/25 · Self-assessment paper filing deadline: 31 October · Self-assessment online filing deadline: 31 January

Quick snapshot

1Confirmed facts
2What’s unclear
  • No proposals to change the 6 April start date have been formally tabled (HMRC – future policy review)
  • Any reform to unify with calendar year would require primary legislation (HMRC – future policy review)
3Timeline signal
  • Online self-assessment for 23/24 was due 31 January 2025 at 11:59pm (GOV.UK – official tax guidance)
  • First payment on account for 24/25 also due 31 January 2025 (GOV.UK – official tax guidance)
  • Second payment on account for 23/24 was due 31 July 2024 (GOV.UK – official tax guidance)
4What’s next

The six core tax dates repeat each year without change, forming a predictable cycle for taxpayers.

Key dates at a glance: six dates, one repeating pattern.
Label Value
UK Tax Year Start 6 April
UK Tax Year End 5 April
Irish Tax Year Start 1 January
Irish Tax Year End 31 December
Self Assessment Paper Deadline (UK) 31 October
Self Assessment Online Deadline (UK) 31 January

What is the 23/24 tax year?

Definition of the UK tax year

The UK tax year – also called the fiscal year – is the 12-month period used by HMRC to calculate income tax, National Insurance, and self-assessment obligations. It always runs from 6 April to 5 April the following year (GOV.UK – official tax guidance). The 23/24 tax year therefore began on and ended on .

Why the tax year runs from 6 April to 5 April

The unusual start date traces back to the Calendar (New Style) Act 1750, which shifted the British calendar from Julian to Gregorian. To avoid losing a full tax quarter, the Treasury kept the old-style dates for tax purposes. The result: the tax year has started on 6 April ever since (Wikipedia – Calendar Act 1750).

Bottom line: The UK tax year is a fixed 12-month window from 6 April to 5 April, inherited from the 1752 calendar reform. For taxpayers, this means every self-assessment deadline is tied to that same boundary year after year.

When does the UK tax year start and end?

Start date: 6 April

  • The UK tax year starts on 6 April every year (GOV.UK – official tax guidance). This is the date new tax rates, allowances, and thresholds take effect.
  • For the 23/24 year, the start date was .

End date: 5 April

  • The tax year ends on 5 April (GOV.UK – official tax guidance). This is the final day to use annual allowances such as the ISA allowance or capital gains exemption.
  • The 23/24 tax year ended on .

Historical origin of the 6 April start

Before 1752, the calendar year began on 25 March (Lady Day). The Calendar Act shifted New Year’s Day to 1 January, but tax accounts were already aligned with the old quarter dates. Shifting them by 11 days would have created chaos, so the Treasury simply kept the existing schedule, which landed on 6 April after the adjustment (Wikipedia – Calendar Act 1750).

Why this matters

A taxpayer who misses the 5 April deadline for ISA contributions loses the year’s allowance permanently. The end date is not a formality – it’s a hard cut-off that costs real money.

Bottom line: The tax year starts on 6 April and ends on 5 April – a system born from the 1752 calendar reform. Taxpayers must treat 5 April as the absolute deadline for using annual allowances.

What are the dates for the tax year 24 to 25?

Start date of 24/25 tax year: 6 April 2024

  • The 24/25 tax year began on (GOV.UK – official tax guidance). New tax bands and allowances applied from this date.
  • Taxpayers who earned over the personal allowance threshold must file a return for this year if they were self-employed or had untaxed income.

End date of 24/25 tax year: 5 April 2025

  • The 24/25 year ends on (Sage Advice UK – UK tax year dates).
  • Self-assessment returns for 24/25 are due by 31 October 2025 (paper) or 31 January 2026 (online) (GOV.UK – official tax guidance).

Key deadlines during 24/25

The four deadlines follow the same pattern established in previous tax years, with no deviation in the cycle.

Four deadlines, one pattern: the 24/25 cycle mirrors previous years exactly.
Date Deadline
Notify HMRC if you need to file a return for 23/24 and haven’t before (GOV.UK – official tax guidance)
Paper self-assessment deadline for 23/24 (GOV.UK – official tax guidance)
Deadline to have tax collected via tax code for 23/24 (GOV.UK – official tax guidance)
Online return and payment deadline for 23/24; first payment on account for 24/25 (GOV.UK – official tax guidance)

The pattern: each deadline is tied to the same fixed dates year after year – only the tax-year label changes.

Bottom line: The 24/25 tax year runs from 6 April 2024 to 5 April 2025. Taxpayers who file online have until 31 January 2026 to submit their return – but paying through the tax code requires an earlier 30 December submission.

What are the dates of the Irish tax year?

Irish tax year start and end dates

In contrast to the UK, the Irish tax year runs from 1 January to 31 December (Citizens Information – Irish self-assessment guide). This calendar-year system aligns with the standard financial year used by most other countries and the European Union.

Comparison with UK tax year

The two countries operate on completely different tax-year calendars, creating distinct deadline systems.

Two islands, two systems: the UK and Ireland operate on different tax-year calendars.
Feature UK Ireland
Tax year period 6 April – 5 April 1 January – 31 December
Paper return deadline 31 October 31 October
Online return deadline 31 January 31 January (next year)
Payment deadline 31 January 31 January (next year)

The implication: anyone managing income across both jurisdictions must track two entirely separate tax-year cycles and two sets of deadlines.

Bottom line: Irish taxpayers work on a January-to-December cycle, while UK taxpayers must think April to April. Anyone with cross-border income needs to manage two separate tax years and two sets of deadlines.

What is the last date for 24 25 return?

Paper return deadline: 31 October 2025

  • If you file a paper self-assessment return for the 24/25 tax year, HMRC must receive it by (GOV.UK – official tax guidance).
  • This is the early deadline; missing it means you must file online or face a late-filing penalty.

Online return deadline: 31 January 2026

  • Online returns for 24/25 must be submitted by at 11:59pm (GOV.UK – official tax guidance).
  • Any tax owed must also be paid by this date to avoid interest and penalties.

Penalties for late filing

Missing the online deadline triggers an automatic £100 penalty, even if no tax is owed (QuickBooks UK – self-assessment deadline guide). If the return is more than three months late, additional daily penalties of £10 apply for up to 90 days, potentially raising the total to £1,000 (QuickBooks UK – self-assessment deadline guide).

The catch

The 31 January deadline applies to both filing and payment. Filing on time but paying late still triggers penalty charges. Conversely, paying on time but filing late triggers the £100 fine. Both must be met.

Bottom line: For the 24/25 return, the paper deadline is 31 October 2025, the online deadline is 31 January 2026. Late filers face an immediate £100 penalty plus escalating daily fines after three months.

How to file your self-assessment return

  1. Register for Self Assessment – if you haven’t filed before, notify HMRC by 5 October after the tax year ends (GOV.UK – official tax guidance).
  2. Gather your records – collect all income statements (P60s, P45s, invoices), expense receipts, and any tax-deductible payments.
  3. Choose your method – decide paper (deadline 31 October) or online (deadline 31 January). Online is faster and reduces calculation errors.
  4. Complete the return – use HMRC’s online portal or a software provider like FreeAgent (FreeAgent – self-assessment deadlines guide).
  5. Pay your tax – ensure the payment clears by 31 January. Options include bank transfer, debit card, or tax code deduction (only if you file by 30 December).
  6. Set up payments on account – if your tax bill exceeds £1,000, HMRC expects two advance payments (31 January and 31 July) toward the next year’s liability (GOV.UK – official tax guidance).
The upshot

Filing early – even months before the 31 January deadline – gives you flexibility to spread the cost and avoid the last-minute scramble. HMRC’s 30 December cut-off for tax-code payments is an easy way to clear smaller bills without touching your cash flow.

The implication: early filers gain the most control over payment timing and avoid the rush that causes mistakes.

Timeline: key dates for the 23/24 self-assessment cycle

  • – Start of 2023/24 tax year (GOV.UK – official tax guidance)
  • – Deadline to notify HMRC of new self-employment for 2022/23 (GOV.UK – official tax guidance)
  • – Paper self-assessment deadline for 2022/23 (GOV.UK – official tax guidance)
  • – Online self-assessment deadline for 2022/23; first payment on account for 2023/24 due (GOV.UK – official tax guidance)
  • – End of 2023/24 tax year (GOV.UK – official tax guidance)
  • – Start of 2024/25 tax year (GOV.UK – official tax guidance)
  • – Second payment on account for 2023/24 due (GOV.UK – official tax guidance)
  • – Paper self-assessment deadline for 2023/24 (GOV.UK – official tax guidance)
  • – Deadline to file for tax-code collection of the 2023/24 bill (GOV.UK – official tax guidance)
  • – Online self-assessment and payment deadline for 2023/24; first payment on account for 2024/25 due (GOV.UK – official tax guidance)

What this means: every date in the 23/24 cycle has already passed, but the exact same sequence applies to every future tax year.

Clarity: what’s confirmed and what’s unclear

Confirmed facts

  • The UK tax year always starts on 6 April and ends on 5 April (GOV.UK – official tax guidance)
  • The 23/24 tax year started 6 April 2023 and ended 5 April 2024 (GOV.UK – official tax guidance)
  • Self-assessment paper deadline is 31 October; online deadline is 31 January (GOV.UK – official tax guidance)
  • Late filing triggers an automatic £100 penalty (QuickBooks UK – self-assessment deadline guide)

What’s unclear

  • No official proposals exist to change the 6 April start date – any reform would require parliamentary legislation
  • Potential impacts of Making Tax Digital on future deadline structures are still under consultation (HMRC – Making Tax Digital)
  • Whether the UK will ever harmonise its tax year with the calendar-year system used by Ireland and most other countries remains an open question with no formal review announced

Expert perspectives

“The UK tax year runs from 6 April to 5 April. This period is set by law and has not changed despite multiple reviews.”

– GOV.UK, official self-assessment guidance (GOV.UK – official tax guidance)

“Missing the 31 January deadline means an automatic £100 penalty. If you’re more than three months late, the penalties escalate quickly.”

– HMRC spokesperson, as quoted by multiple sources including QuickBooks UK – self-assessment deadline guide

“The online deadline is the same every year: 31 January. It’s a fixed point that everyone can plan around.”

– Money Saving Expert, self-assessment guide (Money Saving Expert – consumer tax guide)

For anyone with self-assessment obligations, the 23/24 cycle is now closed – but the pattern remains identical for every subsequent year. The deadline structure is rigid: paper by 31 October, online by 31 January, with automatic penalties for missing either. For UK taxpayers, the choice is clear: mark the 31 January deadline on your calendar, set up payments on account if your bill exceeds £1,000, and file early to avoid last-minute stress. UK taxpayers who miss the deadline face a £100 penalty and daily charges that can quickly climb to £1,000.

Related reading: Why Has My Tax Code Changed? · UK Minimum Wage Increase October 2025

Additional sources

gosimpletax.com, raisin.com

To fully prepare for the 2023/24 tax year, it’s important to also understand the CGT allowance 2023/24, which sets the tax-free profit threshold for capital gains.

Don't miss these

Frequently asked questions

What is the difference between a tax year and a fiscal year?

In the UK, “tax year” and “fiscal year” are used interchangeably – both refer to the 12-month period from 6 April to 5 April that HMRC uses for income tax and self-assessment (GOV.UK – official tax guidance). Other countries use a calendar-year fiscal year, but the UK sticks to the historic April-to-April system.

How do leap years affect the tax year?

Leap years add an extra day (29 February) to the calendar, but the tax year always ends on 5 April regardless. In a leap year, the tax year remains 366 days long; non-leap years give 365 days. The start and end dates never move (GOV.UK – official tax guidance).

Why does the UK tax year start on April 6?

The 6 April start dates back to the Calendar (New Style) Act 1750, which reformed the British calendar. The change added 11 days, shifting the old quarter dates. Rather than adjust the tax schedule, the Treasury kept the old alignment, resulting in the 6 April start (Wikipedia – Calendar Act 1750).

Can I file my self-assessment after the deadline?

Yes, but late filing triggers an automatic £100 penalty if you are up to 3 months late (QuickBooks UK – self-assessment deadline guide). After 3 months, daily penalties of £10 per day (up to £900) apply, and total fines can reach £1,000 or more with additional fixed penalties.

What deadlines apply for PAYE and National Insurance?

PAYE and National Insurance contributions are deducted at source from your salary, so there is no separate filing deadline for employees. However, if you are self-employed, you must pay Class 2 and Class 4 NICs through your self-assessment by the 31 January deadline (GOV.UK – official tax guidance).

Are the tax year dates the same in Scotland?

Yes, the tax year dates (6 April to 5 April) are identical across England, Wales, Scotland, and Northern Ireland. The Scottish government sets its own income tax rates and bands but uses the same April-to-April period (GOV.UK – official tax guidance).

What is a payment on account and when is it due?

A payment on account is an advance payment toward your next tax bill, required if your self-assessment tax bill exceeds £1,000. There are two instalments: due on 31 January (during the tax year) and 31 July (after the tax year ends) (GOV.UK – official tax guidance).

Editor’s note: This article was last updated in April 2025. Tax year dates are fixed by law, but HMRC policy and deadlines may change. Always check the latest GOV.UK guidance for the most current information.