Penalties | Self Assessment
Missed the Self Assessment Deadline? HMRC Penalties Explained (2026)
If you have missed the 31 January Self Assessment deadline, the most useful thing to know is this: the penalty does not stay at £100. It grows, in steps, and the longer the return sits unfiled the worse it gets. The good news is that the growth stops the moment you file, and a genuine reason can sometimes wipe the penalty out completely. Here is exactly what you are facing and what to do about it today.
The single biggest mistake is waiting. Daily penalties and interest accrue while you do nothing. Filing the return, even before you can pay the tax, freezes the late filing penalties where they are.
The Late Filing Penalties, Step by Step
These are charged for sending your return in late. They apply whether or not you owe any tax.
| How late the return is | Penalty |
|---|---|
| 1 day late (missed 31 Jan) | £100 fixed penalty, automatic, even if your bill is £0 or already paid |
| 3 months late | £10 per day for up to 90 days, a maximum of £900, on top of the £100 |
| 6 months late | A further £300, or 5 per cent of the tax due, whichever is higher |
| 12 months late | Another £300, or 5 per cent of the tax due, whichever is higher (more in serious cases) |
Stack those up and a return left unfiled for a year reaches £1,600 or more in late filing penalties alone, before a penny of the actual tax. That is the number that surprises people, and it is why "I will get to it eventually" is the most expensive plan.
Late Payment Penalties Are Separate
Filing late and paying late are two different things, with two different sets of penalties. If you owe tax and have not paid it, you are charged:
- 5 per cent of the unpaid tax if it is still outstanding 30 days after the due date.
- Another 5 per cent at 6 months.
- Another 5 per cent at 12 months.
- Interest on the unpaid tax, accruing daily at HMRC's published rate, from 1 February until you clear it.
So if you both filed late and owe tax you have not paid, you can be hit by both penalty regimes at once. Filing the return deals with the first; a payment or a payment plan deals with the second.
CIS subcontractor, 5 months late, walked away owing nothing
A bricklayer came to us in late June having ignored two HMRC letters since January. He assumed he owed hundreds in penalties and was dreading the bill. He had £100 and the start of daily penalties already showing.
We filed his return that week. Because he had worked under CIS all year and had 20 per cent deducted at source, the return showed he was actually owed a refund. The refund more than covered the £100, and we appealed the daily penalties with a reasonable excuse. He ended up with money back rather than a fine.
Can You Get the Penalty Cancelled?
Often, yes. HMRC will cancel a penalty if you had a reasonable excuse for filing late and you put it right as soon as that excuse ended. Reasonable excuses that HMRC commonly accepts include:
- A serious or life-threatening illness, or the illness of someone you care for.
- A bereavement of a close partner or family member around the deadline.
- A fire, flood or theft that prevented you filing.
- A genuine, documented failure of HMRC's online service or your filing software.
- Postal delays you could not have predicted, or service disruption beyond your control.
What usually does not count: leaving it too late, finding the system too hard, not getting a reminder, or relying on someone else who let you down (unless that was itself outside your control). You appeal online or with form SA370, normally within 30 days of the penalty notice, and you must have filed the outstanding return first.
Even if you have no reasonable excuse, filing immediately is still the right move. It stops the daily penalties, starts the clock on any refund, and lets you set up a Time to Pay arrangement for the tax itself.
What To Do Right Now
- File the return, today if you can. This freezes the late filing penalties. If you are missing your UTR or Government Gateway login, sort that first, see our guide to registering for Self Assessment and getting your UTR number.
- Check whether you are actually owed money. If you work under CIS or had tax taken at source, you may be due a refund rather than a bill. See how to claim a CIS tax refund.
- Pay what you can, or set up a payment plan. HMRC's Time to Pay lets many people spread the bill monthly. Setting one up reduces the sting of the late payment penalties.
- Appeal if you had a reasonable excuse. Do it within 30 days of the penalty notice, after the return is filed.
- If you have stopped trading, tell HMRC so the returns stop too, otherwise penalties keep landing for years you no longer need to file. See how to tell HMRC you have stopped being self-employed.
Frequently Asked Questions
What is the penalty for filing my tax return late?
You get an automatic £100 penalty the moment you miss the 31 January online filing deadline, even if you owe no tax or have already paid. After three months it climbs by £10 a day for up to 90 days (a further £900). At six months late you add £300 or 5 per cent of the tax due, whichever is higher, and the same again at twelve months.
Do I get a penalty if I owe no tax?
Yes. The £100 late filing penalty applies even when your tax bill is zero or has already been paid, because it is a penalty for filing the return late, not for paying late. The only way to avoid it is to file on time, or to have the return cancelled if you did not need to file at all.
Can I appeal an HMRC late filing penalty?
Yes. If you have a reasonable excuse such as serious illness, a bereavement, a fire or flood, or a documented HMRC or software failure, you can appeal, usually online or with form SA370, normally within 30 days of the penalty notice. You must file the outstanding return first and put right whatever caused the delay.
What is the difference between late filing and late payment penalties?
Late filing penalties are charged for sending the return in late and start at a fixed £100. Late payment penalties are separate and charged on tax you owe but have not paid, at 5 per cent of the unpaid tax at 30 days, again at six months, and again at twelve months, with daily interest on top. You can be hit by both at once.
Behind on a tax return? We will sort it fast.
At Your Tax Help Accountants in Stanmore, we file overdue Self Assessment returns, check whether you are owed a refund, appeal unfair penalties and set up payment plans, for subcontractors, drivers, sellers and sole traders across the UK. Fixed fee, no judgement, often faster than you think.
Or email info@yourtaxhelp.co.uk | yourtaxhelp.co.uk
General guidance only. Not personal tax advice. Penalty rules and HMRC interest rates can change. Contact us for advice specific to your situation. All figures are for the 2026/27 tax year unless otherwise stated.