UK Tax Deadlines 2026: Self Assessment, Corporation Tax and Quarterly Payments

Missing a tax deadline in the UK means automatic penalties, interest charges, and — for larger companies — surcharges. This guide sets out every key tax deadline for 2026 and early 2027, covering Self Assessment, Corporation Tax, and quarterly payment obligations.

Self Assessment: key 2026 and 2027 deadlines

Self Assessment is for individuals who are self-employed, directors, or who have income outside PAYE that needs to be reported to HMRC. The tax year in the UK runs 6 April to 5 April.

The 2025/26 tax year (ended 5 April 2026)

Deadline	Date	What it is
Register for Self Assessment	5 October 2026	If you need to file a return for 2025/26 and are not already registered
Paper return deadline	31 October 2026	For those filing a paper Self Assessment return
Online return filing deadline	31 January 2027	File your 2025/26 Self Assessment return online
Balancing payment	31 January 2027	Any remaining tax owed for 2025/26 after payments on account
1st payment on account (2026/27)	31 January 2027	First instalment towards your 2026/27 tax bill (50% of 2025/26 liability)

The key date coming up: 31 July 2026

Before we get to January 2027, there is a significant payment deadline in summer 2026:

• 31 July 2026 — Second payment on account for the 2024/25 tax year. This is the second 50% instalment of your estimated 2024/25 tax bill. If you overpaid, you will receive a refund after filing your 2025/26 return in January 2027.

Penalties for late Self Assessment filing

• 1 day late: £100 automatic penalty
• 3 months late: £10 per day, up to 90 days (£900 maximum)
• 6 months late: 5% of tax owed or £300, whichever is greater
• 12 months late: A further 5% of tax owed or £300, whichever is greater

In addition, HMRC charges late payment interest at the Bank of England base rate plus 2.5% from the due date until payment is made.

Corporation Tax: deadlines for small companies

Corporation Tax is paid by limited companies on their taxable profits. Unlike Self Assessment, you must calculate and pay your Corporation Tax before you file your return.

Key Corporation Tax deadlines for companies with common year ends

Accounting year end	CT payment due (9 months + 1 day)	CT600 filing due (12 months)
31 March 2025	1 January 2026	31 March 2026
30 June 2025	1 April 2026	30 June 2026
30 September 2025	1 July 2026	30 September 2026
31 December 2025	1 October 2026	31 December 2026
31 March 2026	1 January 2027	31 March 2027

These timelines apply to small companies (those not required to pay by quarterly instalments). The current Corporation Tax rate is 25% on profits over £250,000, and 19% (small profits rate) on profits up to £50,000, with marginal relief between.

Quarterly instalment payments (QIPs) for larger companies

Large companies — broadly those with annual taxable profits over £1.5 million — must pay Corporation Tax in quarterly instalments during the accounting period itself, rather than nine months after it ends.

For a company with a 31 March 2026 year end, the four QIP deadlines are:

• Instalment 1: 14 October 2025 (month 7 of the accounting period)
• Instalment 2: 14 January 2026 (month 10)
• Instalment 3: 14 April 2026 (month 13 — first month after year end)
• Instalment 4: 14 July 2026 (month 16)

Very large companies (profits over £20 million) must pay even earlier — instalments begin in month 3 of the accounting period.

Underpaying QIPs attracts interest charges from HMRC at the official rate.

Making Tax Digital for Income Tax Self Assessment (MTD for ITSA)

From April 2026, sole traders and landlords with qualifying income over £50,000 must submit quarterly updates to HMRC using MTD-compatible software — in addition to an annual return. Those with income over £30,000 follow from April 2027.

This means quarterly tax reporting is no longer just for VAT-registered businesses. If you are a sole-trader dealer on the VAT Margin Scheme, you may need to be filing quarterly income tax updates from April 2026 as well as your quarterly VAT returns.

All key 2026 tax deadlines at a glance

Date	Obligation
7 May 2026	VAT return filing and payment — Q1 2026 (Stagger 1)
31 July 2026	Self Assessment 2nd payment on account (2024/25)
7 August 2026	VAT return filing and payment — Q2 2026 (Stagger 1)
5 October 2026	Register for Self Assessment (if new, for 2025/26)
31 October 2026	Self Assessment paper return deadline (2025/26)
7 November 2026	VAT return filing and payment — Q3 2026 (Stagger 1)
31 January 2027	Self Assessment online return + balancing payment + 1st payment on account (2025/26)
7 February 2027	VAT return filing and payment — Q4 2026 (Stagger 1)

Always verify specific deadlines with your accountant or directly on HMRC's deadline pages, as dates can shift when they fall on weekends or bank holidays.

The link between tax deadlines and your bookkeeping

Every tax and filing deadline above is driven by accurate, complete bookkeeping records. For second-hand dealers using the VAT Margin Scheme, that means maintaining a compliant stockbook with every purchase and sale recorded at the time of the transaction — not reconstructed at quarter-end.

Dealers who try to pull records together at filing time consistently miss deadlines, make errors, and attract HMRC enquiries. AutoVAT eliminates the problem by keeping your VAT Margin records accurate and up to date automatically, so when a deadline arrives, your numbers are already ready.