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Updated for 2026/27
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HMRC Self Assessment Deadlines & Penalties 2026/27

Don't get hit with a £100 fine. See every critical date for registration, filing, and payment in the current UK tax year.

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TaxWiz Editorial

Tax Content Writer • Modified 2026-04-09

HMRC Deadlines: Stay Legit in 2026/27

The UK tax system is strict about dates. HMRC operates an automated penalty system—missing a deadline by even one minute results in an instant fine, regardless of whether you actually owe any tax.

The Short Answer

The most important date is January 31st.

This is the absolute deadline for filing your online return AND paying any tax owed. If you miss this, you lose £100 immediately.

Important: Which year are you filing for?

Because the UK tax year runs behind, the deadlines you face in 2026/27 are actually for your work done in the previous tax year (2025/26).

The 2026/27 Calendar (For 2025/26 Tax Returns)

Here are the critical milestones if you earned over £1,000 between April 6, 2025 and April 5, 2026:

DateMilestoneWhat it means
April 6, 20262026/27 BeginsNew year for receipt tracking
July 31, 2026Payment on AccountSecond payment for established traders
October 5, 2026Registration DeadlineLast day to tell HMRC you're a business
October 31, 2026Paper DeadlineOnly if you still file via physical post
December 30, 2026PAYE DeadlineFor tax collection from your day job salary
January 31, 2027The Big OneFinal day to file online and pay your tax

Penalties and Fines

HMRC's fines are progressive. The longer you wait, the more expensive it gets:

  • 1 Day Late: An instant £100 fixed penalty.
  • Up to 3 Months Late: £10 per day for up to 90 days (max £900).
  • 6 Months Late: A further £300 or 5% of the tax due (whichever is higher).
  • 12 Months Late: Another £300 or 5% of the tax due.
In Plain English

What is "The 'Reasonable Excuse'"?

HMRC will only cancel a fine if you have a serious excuse, such as a death in the family, a serious illness, or a technical failure on their side. Forgetting or being 'too busy' is not accepted.

First-Time Filers: A Warning

If this is your first year as an online seller, creator, or freelancer, do not wait until January to register.

It can take up to 15 working days for HMRC to process your registration and send your UTR Number (Unique Taxpayer Reference) through the post. Without this number, you cannot file, and you will be fined even if you have the login ready.

Need to Register?

  • Get your UTR Number well before the January deadline.
  • Avoid the £100 automated late-filing fine.
  • Set up your Government Gateway account securely.
See the Registration Guide
Disclaimer: Tax rules and deadlines are subject to change by HMRC. Always verify your specific situation on the official GOV.UK website.

Frequently Asked Questions

Yes. If you are registered for Self Assessment, you must file a 'Nil' return even if you made £0 profit, unless you formally close your business with HMRC.
HMRC offers 'Time to Pay' arrangements if you owe less than £30,000. You can set this up online to pay in installments.

Tax Disclaimer: TaxWiz provides general educational information and guides for UK residents. While we strive to maintain accuracy for the 2026/27 tax year, tax rules are subject to change. This content does not constitute regulated financial, legal, or tax advice. For complex situations, we strongly recommend consulting a qualified UK accountant. View our full Disclaimer.