HMRC’s official figures released shortly after the January deadline estimated that around one million taxpayers missed the filing deadline for the 2024/25 tax year.
While many will have filed in the weeks that followed, those who have still not submitted their 2025 Self-Assessment tax return could be in for a significant financial shock. From 1st May 2026, HMRC moves into a much stricter penalty phase - and costs can escalate quickly.
Daily penalties are about to begin: the £10-a-day countdown
If you have not yet filed your return, you will likely already have received the initial £100 late filing penalty, which is automatically applied after the 31st January deadline.
However, if the return remains outstanding by midnight on 30th April, the penalty regime becomes far more serious.
From 1st May 2026, HMRC introduces daily penalties, meaning the cost of delay increases every single day.
Here are some more details:
1. The daily penalty: £10 per day
Once your tax return is three months late, HMRC begins charging £10 per day for each day the return remains unfiled.
This means:
- Delaying for a further three months could result in £900 in additional penalties.
- The charges apply regardless of whether you owe tax or are due a refund.
- This is an important point - the penalty is not just about unpaid tax. It is a penalty for failing to submit the required documentation on time.
2. The late payment ‘double whammy’
It is also important to distinguish between filing your return and paying any tax due - they are treated separately by HMRC, and both can trigger penalties.
If you still owe tax for the 2024/25 year:
- A penalty of 5% of the unpaid tax will already have been applied from 2nd March 2026 (30 days late).
- HMRC is also charging interest on late payments, currently at 7.75%, calculated daily from the original due date of 31st January 2026.
- This means that the longer the delay continues, the more the total liability increases - not just through fixed penalties, but through ongoing interest charges.
3. What happens if you continue to delay?
If daily penalties are not enough to prompt action, further penalties apply at key points in the year.
From 1st August 2026 (six months late):
- An additional penalty of £300 or 5% of the tax due (whichever is higher) will be charged.
- A further £300 or 5% of the tax due (whichever is higher) will apply
From 1st February 2027 (twelve months late):
In more serious cases, where HMRC believes there has been deliberate withholding of information, penalties can increase significantly — potentially up to 100% of the tax due.
Why acting now matters
The key takeaway from this should be that penalties escalate quickly and automatically. What starts as a £100 fine can rapidly grow into a much larger financial burden if left unaddressed.
Importantly, HMRC does not require intent or wrongdoing to apply these penalties - they are triggered simply by missing deadlines.
For many taxpayers, the situation can feel overwhelming, particularly if there are uncertainties around income, records or tax calculations. However, delaying further will only increase the cost and complexity of resolving the issue.
How Coles Miller can help
If you have not yet filed your tax return, it is important to act as soon as possible.
We can assist by reviewing your position, helping you complete and submit your return accurately, and advise on any penalties that may have been applied. Where appropriate, we can also explore whether there are grounds to challenge or reduce penalties, particularly if there are mitigating circumstances.
Don’t let a small delay become a bigger problem
With the 1st May deadline fast approaching, the window to avoid daily penalties is closing.
Taking action now can help prevent a relatively modest £100 penalty from turning into a much more significant financial issue.
If you need support or advice, our experienced team can help you resolve matters quickly and confidently.
