If you need to file a Self Assessment tax return, deadlines matter. HMRC penalties are automatic, and missing a date can cost you money even if you owe very little tax.
This guide explains the UK Self Assessment deadlines for the 2024-2025 tax year, the difference between filing and payment dates, and exactly what happens if you file late.
Key Self Assessment deadlines for 2024-2025
There are two deadlines you must understand.
Filing deadline
This is the date your tax return must be submitted to HMRC.
Payment deadline
This is the date any tax owed must be paid.
You can file on time and still be late paying. HMRC will still charge interest and penalties.
Important dates
- 31 October 2025 – Paper tax return deadline
- 31 January 2026 – Online tax return deadline
- 31 January 2026 – Tax payment deadline, including:
- Any tax owed for 2024-2025
- First Payment on Account (if required)
👉Unsure which deadlines apply to you?
Book a consultation with Tax2u and we’ll confirm everything for you.
Paper vs online tax return deadlines
Different HMRC UK Self Assessment deadlines applies deadlines depending on how you file.
Paper tax returns
- Deadline: 31 October 2025
- Miss this and HMRC expects you to file online
- Penalties still apply if the paper return is late
Online tax returns
- Deadline: 31 January 2026
- This is the most common method
- This date also covers your tax payment
Leaving your return until January increases risk. Errors are harder to fix, and HMRC systems are often slow.
What happens if you miss the deadline?
HMRC late filing penalties are automatic. There is no warning period.
1 day late
- £100 fixed penalty
- Applies even if:
- You owe no tax
- You are due a refund
30 days late
You will be charged:
- The £100 fixed penalty
- Plus £10 per day for up to 90 days
- Maximum additional charge: £900
Penalties increase quickly at this stage.
6 months late
HMRC adds another penalty:
- £300 or
- 5% of the tax owed (whichever is higher)
This is added on top of earlier penalties.
12 months late
HMRC may charge:
- Another £300 or 5% of tax owed
- Or up to 100% of the tax due in serious cases
HMRC may also:
- Issue estimated tax bills
- Open a compliance check
- Start debt recovery action
Late payment penalties and interest
Filing on time does not protect you from payment penalties.
From 1 February 2026, HMRC will:
- Charge daily interest on unpaid tax
- Add late payment penalties:
- 5% after 30 days
- 5% after 6 months
- 5% after 12 months
If you cannot pay in full, HMRC may allow a Time to Pay arrangement. Acting early is key.
Why you shouldn’t leave filing until January
Filing early gives you:
- Time to fix mistakes
- Clarity on what you owe
- Fewer penalties
- Less stress
If you are unsure whether you need to file, what documents are required, or how late penalties apply, getting help early makes a real difference.
👉Register with Tax2u today and get your Self Assessment sorted before deadlines cost you more than necessary.