Staying on top of tax deadlines is one of the most important responsibilities for UK business owners. Missing a filing or payment date can result in automatic penalties, interest charges, and unnecessary stress — particularly if issues are only discovered after HMRC has been in touch.
At Atreus Accountants, we work with business owners across London and the UK, helping them stay compliant, organised, and prepared well in advance. This guide sets out the key UK tax deadlines for 2026, who they apply to, and how to prepare properly.
Who This Guide Is For
This article is relevant if you are:
- A sole trader required to submit a Self Assessment tax return
- A limited company director responsible for Corporation Tax
- A VAT-registered business operating under Making Tax Digital
- An employer running payroll and PAYE
If you fall into any of these categories, the deadlines below will apply to you.
Self Assessment Tax Deadlines (Sole Traders & Company Directors)
If you submit a Self Assessment tax return, these are the most important dates to be aware of:
- 31 January 2026
- Deadline for submitting your online Self Assessment tax return
- Deadline for paying:
- Any tax owed for the 2024/25 tax year
- Your first payment on account for the 2025/26 tax year (if applicable)
- 31 July 2026
- Deadline for your second payment on account (where required)
Missing the January deadline results in an automatic £100 penalty, even if no tax is owed. Additional penalties and interest apply the longer the return remains outstanding.
👉 Many clients choose to outsource this entirely via our Self Assessment services to avoid last-minute pressure and errors.
Corporation Tax Deadlines for Limited Companies
Corporation Tax deadlines are based on your company’s accounting period rather than the tax year.
- Corporation Tax payment
- Due 9 months and 1 day after the end of your accounting period
- CT600 (Company Tax Return)
- Must be filed within 12 months of the end of your accounting period
Example
If your accounting year ends on 31 March 2025:
- Corporation Tax payment due: 1 January 2026
- CT600 filing deadline: 31 March 2026
Late filing or payment can trigger penalties, interest, and HMRC compliance checks.
👉 Support with this is typically included within our Limited Company Accounting and Corporation Tax services.
VAT Return Deadlines & Making Tax Digital
Most VAT-registered businesses submit VAT returns quarterly.
- VAT returns and payments are due 1 month and 7 days after the VAT period end
- All VAT submissions must comply with Making Tax Digital (MTD) rules
Common VAT quarter ends:
- 31 March
- 30 June
- 30 September
- 31 December
Under HMRC’s VAT penalty system, late submissions can result in penalty points and financial charges, even if no VAT is owed.
👉 We help clients stay compliant through our VAT and Making Tax Digital support, including software setup and ongoing reviews.
Payroll, PAYE & Employer Deadlines
If you operate payroll, there are ongoing monthly and annual obligations:
- RTI submissions
- Must be filed on or before each employee’s pay date
- PAYE & National Insurance payments
- Due by the 22nd of the following month when paid electronically
- P60s
- Must be issued to employees by 31 May 2026
- P11D / P11D(b) (where applicable)
- Deadline: 6 July 2026
Payroll errors are one of the most common causes of HMRC queries, particularly where reporting is inconsistent.
👉 Many businesses choose to outsource this entirely using our Payroll services to ensure accuracy and compliance.
Common Mistakes That Lead to HMRC Penalties
In our experience, penalties often arise due to:
- Leaving returns until January
- Assuming no profit means no filing requirement
- Incomplete or outdated bookkeeping
- Forgetting payments on account
- Cash flow issues affecting VAT payments
Most of these issues are entirely preventable with proper planning.
How to Prepare for 2026 Tax Deadlines
To stay compliant and reduce stress:
- Keep bookkeeping up to date throughout the year
- Use cloud accounting software that integrates with HMRC
- Review your tax position well before deadlines
- Plan for upcoming tax liabilities in advance
- Speak to an accountant early — not when deadlines are imminent
Proactive planning allows you to reduce tax legally, manage cash flow more effectively, and avoid last-minute decision-making.
👉 Our bookkeeping and cloud accounting services are designed to support this year-round.
How Atreus Accountants Can Support Your Business
At Atreus Accountants, we work with sole traders, limited companies, and growing businesses across London and the UK. Our focus is on proactive advice, clear communication, and ensuring nothing is left to chance.
We help clients:
- Meet all HMRC filing and payment deadlines
- Stay compliant with tax and reporting obligations
- Improve financial visibility
- Plan ahead with confidence
Need Help Staying Compliant in 2026?
If you’d like support with tax returns, bookkeeping, VAT, or payroll, get in touch with Atreus Accountants to discuss how we can help. Early planning makes all the difference.