You’ll normally receive an automatic penalty from HMRC if you need to submit a Self Assessment tax return and miss the filing or payment deadline. In this article we go over what deadlines are in place, the Self Assessment penalty system, and what to do if you can’t pay your tax bill.
When do I need to submit my Self Assessment tax return?
The Self Assessment submission deadline varies depending on whether you’re submitting an online or paper return, as well as how you plan to pay.
| Action | What you need to do | Deadline |
| Register for Self Assessment | If you need to send a tax return for 2025/26 but didn't need to for the previous year, you should register for Self Assessment by this date. | 5th October 2026 |
| Submit a paper tax return | The deadline for submitting your Self Assessment tax return if you use a paper form. | Midnight, 31st October 2026 |
| Submit a tax return if you want to pay your bill through PAYE | Request that HMRC collect any tax you owe through your tax code | Midnight, 30th December 2026 |
| Submit a tax return online | This is the deadline for submitting your tax return if you submit online. | Midnight, 31st January 2027 |
| Pay your Self Assessment tax bill | You should pay your tax bill in full by this date in order to avoid penalties. | Midnight, 31st January 2027 |
How much is the fine for late Self Assessment filing?
You’ll be hit by an automatic £100 penalty from HMRC if you miss the deadline to file your Self Assessment tax return. The fine becomes larger the longer you leave it before taking action.
Failure to submit within three months of the deadline (by the end of April) incurs an additional £10 a day fine for the next 90 days. This means the penalty will increase by £900 – bringing the total penalty to £1,000. Ouch.
A further penalty of either £300 or 5% of the tax owed (whichever is higher) will be applied if the submission is 6 months late, and then again at 12 months.
What if I didn’t need to submit a tax return?
HMRC expect a Self Assessment return from anyone who is registered to submit one. Unless you tell them otherwise and let them know in advance, you’ll receive a penalty for failing to submit.
Self Assessment late payment penalties and fines
As well as penalties for missing the Self Assessment submission deadline, there are fines for missing the payment deadline too. We explain the penalties in the table below.
| How many days the payment is overdue | Penalty |
| 30 days late | Your tax bill, plus an additional penalty of 5% of what you owe, plus interest on what you owe |
| 6 months late | The above, plus 5% of that amount, plus interest on what you owe |
| 12 months late | The above, plus a further 5% of that amount, plus interest on what you owe |
Payments on account penalties
Payments on account are intended to spread the cost of paying your Self Assessment income tax and Class 4 National Insurance contributions. If your tax bill is more than £1,000 for a tax year, you’ll be required to make payments on account towards the following tax year.
It’s basically an advance payment on next year’s bill, working on the assumption that your earnings will be the same as (or higher) than the previous year.
The idea behind it is that you don’t have to pay one massive bill in January. In practice it means that you will pay 50% of the previous year’s bill as an advance against tax for the following tax year.
The deadline to pay the first instalment is the same as the deadline to pay your tax bill for the previous year (so it can come as a bit of a shock). The second instalment is due by 31st July and, just like the January deadline, missing the July payment date also incurs penalties.
What if I can’t afford to pay my tax bill?
You might be able to make a Time to Pay arrangement if you’re having problems paying your tax bill on time. This is basically a payment plan which allows you to make affordable monthly payments towards your tax bill if you’re struggling.
Can I appeal a Self Assessment penalty?
HMRC will sometimes waive penalties if you have a “reasonable excuse”, though they’re pretty strict on what counts. It’s largely down to their discretion, though you may be excused if you’ve been seriously ill, suffered a bereavement close to the deadline, or you’ve had serious IT problems.
You can also appeal against a penalty you think was unfairly given, using a SA370 form or the online service.
Talk to one of the team about our online accounting services, including tax returns. Call 020 3355 4047 and get an instant online quote.
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