Self Assessment Deadlines for the 2025/26 UK Tax Year

For individuals with income outside PAYE, Self Assessment remains a key compliance obligation under the UK tax system. This includes self-employed individuals, company directors, landlords, and those with investment or overseas income. Understanding the deadlines for the 2025/26 tax year—which runs from 6 April 2025 to 5 April 2026—is essential to avoid unnecessary penalties and interest.

Registering for Self Assessment

If you are required to submit a Self Assessment tax return for the first time for the 2025/26 tax year, you must notify HM Revenue & Customs (HMRC) by 5 October 2026. Registration enables HMRC to issue a Unique Taxpayer Reference (UTR), which is mandatory for filing a return. Late registration can delay your ability to file and may result in compliance issues, particularly where tax is due.

Our firm regularly assists new clients with Self Assessment registration, ensuring the process is completed accurately and on time.

Tax Return Submission Deadlines

HMRC offers two methods for submitting a Self Assessment tax return: paper and online. Each has a different deadline:

• Paper tax returns must reach HMRC by 31 October 2026.

• Online tax returns must be submitted by 11:59 pm on 31 January 2027.

  
  

Online filing is generally the preferred option, offering greater flexibility, built-in validation checks, and a later submission deadline. It also allows taxpayers to review their tax position earlier and plan cash flow more effectively.

Payment of Tax Liabilities

Any tax owed for the 2025/26 tax year must be paid by 31 January 2027. This includes the balancing payment for the year and, where applicable, the first Payment on Account towards the following tax year. Payments on Account commonly apply to self-employed individuals and certain landlords.

If Payments on Account are required, the second instalment will usually be due by 31 July 2027.

Penalties for Late Filing and Payment

HMRC applies an automatic £100 late filing penalty if a tax return is submitted after the deadline, even where no tax is payable. Further daily penalties, interest, and surcharges may apply if delays continue. Late payment of tax also incurs interest from the day after the due date.

How We Can Help

Our accounting team supports clients throughout the Self Assessment process—from registration and record-keeping to accurate submission and tax planning. By engaging early, we help minimise risk, manage liabilities efficiently, and ensure full compliance with HMRC requirements.

If you would like assistance with your 2025/26 Self Assessment tax return, please contact our team to discuss how we can support you.