What Happens If You Miss the Tax Return Deadline?
Chrissy Leach • 5 January 2026
Understand HMRC’s penalty and interest rules, and why it pays to file your return on time.
If you’re one of the millions of people who need to complete a Self Assessment tax return, the key date to remember is 31 January 2026 (for the 2024/25 tax year). That’s the deadline to file your return and pay any tax due to HMRC.
At CJL Accountancy, we always encourage clients to submit their returns early where possible, but if you haven’t done it yet, there’s still time. Here’s what happens if you miss the deadline, and why acting quickly can save you money and stress.
What happens if you miss the Self Assessment deadline?
If your tax return isn’t submitted by midnight on 31 January, HMRC will automatically issue a £100 late filing penalty, even if you don’t owe any tax.
After that, further penalties apply:
- 3 months late: £10 per day, up to a maximum of £900
- 6 months late: An additional £300 (or 5% of the tax due, if higher)
- 12 months late: Another £300 (or 5% of the tax due, if higher)
These penalties can add up quickly, especially if you miss multiple deadlines.
Late payment penalties
HMRC also charge penalties for paying your tax late, whether your tax return is filed or not. These are:
- 5% of the tax unpaid after 30 days
- Another 5% after 6 months
- A final 5% after 12 months
It's worth noting that you can make a tax payment even if you haven't filed your tax return, which can help reduce penalties.
Interest charges on late tax payments
HMRC will start charging interest from 1 February
on any outstanding tax. The interest rate will be 7.75% from 9 January 2026 (it's 4% above the Bank of England base rate).
Can you appeal?
If you have a reasonable excuse - for example, serious illness or technical issues with HMRC’s system - you can appeal a late filing or late payment penalty. However, HMRC is strict about what counts as reasonable, so it’s best not to rely on this. If you’re appealing on technical issues, keep screenshots or videos of the errors you encounter.
Interest charges, however, are very difficult to appeal because they’re designed to compensate HMRC for the late payment and reflect the benefit you had from holding onto the funds.
Time-to-pay
You can set up a time-to-pay arrangement with HMRC if you can't make the full tax payment on time. You can either do this in your online self-assessment account or by contacting HMRC. Penalties are suspended if you have a time-to-pay agreement, as long as you stick to the agreed terms.
What should I do if I haven't filed my return yet?
You still have some time; try to prepare and file your tax return and pay your tax by 31 January. If that's not possible:
- File a provisional return by 31 January: If you're waiting for information to finalise your tax return then file with the information you do have and perhaps an estimate of what you're waiting for. You have 12 months to file your final return.
- Make a payment on account: If you're not sure what your final tax figure is, make an estimated payment on account to reduce interest and penalties.
How to avoid penalties and reduce stress
- File early: In the future, even if you wait to pay until January, filing early gives you time to plan your tax bill.
- Check your details: Make sure HMRC has your up-to-date address so you don’t miss important letters.
- Use professional support: An accountant can help you submit accurately and claim all allowable expenses.
- Plan for payment: Set aside funds throughout the year to avoid a cash flow shock in January.
If you’re not sure where to start, CJL Accountancy
can help you complete your return quickly and accurately so you can avoid penalties.
Please note: We cannot guarantee meeting the 31 January filing deadline for clients signing up in January. However, we may be able to reduce interest and penalties
by preparing your return soon after.
For the 2025/26 tax year, we’ll work with you to get things completed early.
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