Guides › Registered for Self Assessment After 5 October? Your Dates
Registered for Self Assessment After 5 October? Your Dates
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Not tax advice. Information only. Check GOV.UK or a qualified adviser for your own situation. Dates and rules were last checked against GOV.UK on 17 October 2026 and can change.
Short answer: GOV.UK says you must tell HMRC by 5 October if you need to complete a return for the previous year and you haven't sent one before (or you registered before but didn't need a return for 2024 to 2025). If you register after 5 October 2026, HMRC sends a letter or email with a different filing deadline: 3 months from the date on the letter or email. You must still pay the tax you owe by 11:59pm on 31 January 2027 or you'll get a penalty.
Putting that into dates (made-up example)
If the letter is dated 20 November 2026, three months from that date is 20 February 2027. The tax is still due on 31 January 2027, a few weeks earlier. (Our arithmetic; use the date on your letter.)
"Failure to notify" penalty
GOV.UK's penalties page says that if you register after 5 October and don't pay all of your tax bill by 31 January, you may get a "failure to notify" penalty based on the amount left unpaid, received within 12 months after HMRC receives your return.
Steps
- Register as soon as you realise you need to.
- Gather income and expense records.
- Put the tax payment date (31 January 2027) in your diary.
- File well before your personal deadline.
Do you need to file at all?
See Do I need to file a return for 2025-26?.
FAQ
Does the 3 months give me extra time to pay? No; GOV.UK says you must still pay by 31 January.
Is the later deadline automatic? HMRC sends the date after you register.
What we could not verify
- How HMRC calculates the exact date if you register late in January or later.
- The registration page itself (we linked, not read in detail).
Sources (GOV.UK)
- GOV.UK, Self Assessment tax returns: Deadlines — https://www.gov.uk/self-assessment-tax-returns/deadlines (read 17 October 2026)
- GOV.UK, Self Assessment tax returns: Penalties — https://www.gov.uk/self-assessment-tax-returns/penalties (read 17 October 2026)
- GOV.UK, Self Assessment tax returns: Who must send a tax return — https://www.gov.uk/self-assessment-tax-returns/who-must-send-a-tax-return (read 17 October 2026)
Deadlines calendar → Penalty estimator →
Not tax advice. See the disclosure.