Quick Summary
- Miss 31 January and HMRC charges an automatic £100 penalty, even if you owe no tax.
- After 3 months, £10 a day is added for up to 90 days — so file as soon as possible.
- Late payment brings separate penalties and interest at Bank of England base rate plus 4%.
- Can't pay in full? You can usually set up a Time to Pay plan online if you owe £30,000 or less.
- Appeal within 30 days of a penalty notice if you had a reasonable excuse.
The online Self-Assessment deadline is 31 January — for the 2025/26 tax year, that's 31 January 2027. If you've missed it, don't ignore the problem: penalties grow the longer a return is outstanding. Here's exactly what happens and what to do.
Late filing penalties
| How late | Penalty |
|---|---|
| 1 day late | £100 fixed penalty |
| 3 months late | £10 a day for up to 90 days (maximum £900) |
| 6 months late | 5% of the tax due or £300, whichever is higher |
| 12 months late | Another 5% or £300, whichever is higher (more if information was deliberately withheld) |
So a return filed 6 months late can cost at least £1,300 in penalties before any tax or interest. Filing even a few weeks late keeps it to £100.
Late payment penalties and interest
Paying late is treated separately from filing late. If tax is still unpaid 30 days after it was due, HMRC adds a penalty of 5% of the unpaid tax, with further 5% penalties at 6 months and 12 months. Interest is charged on top from the due date, at the Bank of England base rate plus 4%.
Sole traders and landlords who have joined Making Tax Digital for Income Tax are moving to a new points-based penalty system for later tax years, but the penalties above apply to most people filing for 2025/26.
What to do now
- File the return as soon as you can. This stops the daily penalties starting and shows HMRC exactly what you owe. Use estimates only where you have to, and correct them later.
- Pay what you can. Any payment reduces the interest building up.
- Set up a payment plan if you need one. If you owe £30,000 or less, have no other tax debts or payment plans, and your returns are up to date, you can usually set up a Time to Pay arrangement online. Above that, call HMRC.
- Check whether you can appeal. See below.
Appealing a penalty: what counts as a reasonable excuse?
You can appeal within 30 days of the date on the penalty notice. HMRC may accept a reasonable excuse such as:
- A serious illness or hospital stay that stopped you dealing with your affairs
- The death of a partner or close relative shortly before the deadline
- An HMRC online service failure
- A fire, flood or theft that destroyed your records
- Unexpected postal delays, or a disability that made filing impossible
Being too busy, finding the system hard or relying on someone who let you down usually isn't enough on its own. You must also have filed as soon as possible once the excuse ended. Our penalty appeal guide covers this in more detail.
What if I didn't need to file?
If HMRC asked you to file but you no longer need to — for example you stopped self-employment and have only PAYE income — contact HMRC to ask them to withdraw the notice to file. If they agree, the penalty is cancelled.
Several years behind?
If you haven't filed for a number of years, it's better to come forward than wait for HMRC to contact you. Penalties are usually lower for voluntary disclosure. An accountant can rebuild your figures from bank statements and invoices and file all the outstanding returns together.
Frequently Asked Questions
What is the penalty for missing the Self-Assessment deadline?
An automatic £100 penalty applies the day after the 31 January deadline, even if you owe no tax. Further penalties are added at 3, 6 and 12 months if the return is still outstanding.
Can I still file my tax return after 31 January?
Yes. You can file online after the deadline, and you should do so as soon as possible to stop daily penalties starting after 3 months.
Can I pay my tax bill in instalments?
Often, yes. If you owe £30,000 or less, have filed your returns and have no other payment plans or tax debts, you can usually set up a Time to Pay plan online.
How long do I have to appeal a late filing penalty?
You must appeal within 30 days of the date on the penalty notice, explaining your reasonable excuse and showing you filed as soon as possible after it ended.
Does HMRC charge interest on late tax?
Yes. Interest is charged on unpaid tax from the due date at the Bank of England base rate plus 4%, as well as any late payment penalties.
Missed the Deadline? We Can Help Today
We file late and overdue tax returns quickly, check whether you can appeal any penalties and help set up an HMRC payment plan.
Sardar Muhammad, AAT
Sardar is the founder of LimeTree Accounting Solutions, an AAT-accredited practice in Govanhill, Glasgow. He works with sole traders, tradespeople, landlords and small limited companies across Glasgow and Clydebank.
This guide is general information based on UK and Scottish tax rules as at 13 October 2026. It is not personal advice. Rates and thresholds change, so speak to us about your own situation.