What are the Self Assessment deadlines?
To avoid incurring any penalties, make sure you note down these important deadlines, as well as the key tax dates.
5 October: Register for Self Assessment
31 October: Filing deadline for paper tax returns
31 January: filing deadline for online tax returns
31 January: deadline for paying the tax you owe
What are the current Self Assessment penalties?
There are different types of penalties depending on whether you make a late payment or fail to register in time.
Registration (failure to notify) penalties
HMRC may penalise you for failing to register for Self Assessment or notify them of any changes that affect your tax liability.
If you’re eligible to register for Self Assessment, you must do so by the assigned deadline (currently 5 October).
If you fail to notify HMRC about anything affecting what you owe in taxes, you can be hit with what’s called a “failure to notify” tax penalty. This applies to things like a new source of income that’s subject to tax or any capital gains you realise during the tax year (including offshore).
As with errors, failure to notify penalties take into account potential lost revenue (PLR). And the fines depend on whether your disclosure of the information is prompted or unprompted. The following table outlines the costs of failure to notify penalties.
Type of behaviour | Unprompted disclosure (Cost as % of PLR) | Prompted disclosure (Cost as % of PLR) |
|---|
| 0-30% (within 12 months) 10-30% (12+ months) | 10-30% (within 12 months) 20-30% (12+months) |
| 0-30% in the first 12 months (10-30% after that) | 0-30% in the first 12 months (20-30% after that) |
| | |
Concealed deliberate error | | |
Learn more about failure to notify penalties.
Self assessment late filing penalties
Remember, you will be penalised for filing your Self Assessment tax return late, even if you don’t owe any tax.
The table below outlines the costs of missing these deadlines:
Date | Penalty |
|---|
| |
| Charges of £10 per day, up to a maximum of £900 |
| Further penalty of £300 or 5% of the tax due (whichever is greater) |
| Another £300 or 5% of the tax due (whichever is greater) |
You can get help filing your return at GOV.UK.
Self assessment late payment penalties
Penalties for late payment only apply if you owe tax. If you miss the deadline for paying your tax liabilities, HMRC will charge you interest on the amount due. The charge is automatic and begins accruing as soon as you miss the deadline. From 6 April 2025, the interest rate on late payments increased to the Bank of England base rate plus 4% (currently 7.75% as of January 2026).
The table below shows the costs and when they’re accrued.
Date | Penalty |
|---|
| |
| Additional fine of 5% of the tax due |
| Additional fine of 5% of the tax due |
Find out what happens if you don’t pay your tax bill at GOV.UK.
Penalties for errors in Self Assessment tax return
HMRC may penalise you for errors on returns or other paperwork that misstate or underestimate what you owe in taxes. You can also be penalised if you receive an incorrect assessment from HMRC and fail to correct the error.
The penalty incurred depends on the type of behaviour cited and the assessment of taxpayer culpability. HMRC sorts behaviours they consider into the following four categories:
Genuine error: You took reasonable care to correctly report your income and taxes (for example, if you submitted the wrong form but filled it out correctly).
Error due to negligence: A mistake resulted from failure to take reasonable care to report or pay taxes.
Deliberate errors: You made a mistake on purpose but did not attempt to hide it.
Concealed deliberate error: You made a deliberate error and made arrangements to conceal the mistake. Charges also depend on whether you come forward to disclose the error yourself.
The penalties are then split into unprompted or prompted disclosure:
Unprompted disclosure means you communicate the errors before HMRC sends you a penalty notice or starts an inquiry into your records
Prompted disclosure means HMRC has started an enquiry into your records and contacted you about an error
Once it determines behaviour and culpability, HMRC calculates costs as a percentage of potential lost revenue or the amount of tax you still need to pay once the error has been corrected. The table below outlines the range of errors and the penalties.
Type of behaviour | Unprompted disclosure | Prompted disclosure (Cost as % of PLR) |
|---|
| | |
| | |
| | |
Concealed deliberate error | | |
What happens if you need to change your return?
If you’ve made a genuine mistake and need to amend your return after you’ve filed it, you can.
Your tax bill will be updated based on the changes you make, so you may find you’ll have to pay more or you could be eligible for a refund.
You’re able to make a change within 12 months of the Self Assessment deadline. You can do this online or by sending another paper return.
Learn more about corrections at GOV.UK.
Appealing Self Assessment penalties
If you feel that your self assessment penalty was wrongly calculated, or that there was a reason you couldn’t pay it, then it’s possible to file a self assessment penalty appeal. HMRC refers to reasons that you couldn’t pay as ‘reasonable excuses’:
The death of a partner or close relative shortly before the deadline
An unexpected stay in hospital that prevented you from submitting your return
You had a serious or life-threatening illness
Your computer or software failed while you were preparing your return
Issues with HMRC’s online services
A fire, flood or theft prevented you from submitting your tax return
Unforeseen postal delays
Delays related to disability
A person you were relying on to complete your tax return didn’t do it
The following excuses, however, won’t be accepted:
Your cheque bounced or payment failed
You found the online system too difficult
You didn’t receive a reminder from HMRC
You made a mistake on your tax return
You can appeal your self assessment penalty within 30 days of the penalty notice being sent to you, and can also appeal by post. Once you submit your appeal, an HMRC officer not involved in the original penalty will investigate it. The investigation will usually take 45 days. In the meantime, you don’t need to pay the fines and won’t face any further penalties until the appeal has been settled.
You can make a second appeal if you still think the decision was wrong. This can be done via the tax tribunal at GOV.UK.
Alternatively, if your tax appeal didn’t succeed through HMRC, you can apply for alternative dispute resolution (ADR). In ADR, you avoid a court hearing by having an impartial third party mediate between you and HMRC. You, or your agent or tax advisor, can use an online form to apply.
Changes to Self Assessment penalties
Following the introduction of a points-based penalty system introduced from the 1st of January 2023 (already applied to VAT from January 2023), the same system will apply to Self Assessment from April 2026 for those brought into Making Tax Digital for Income Tax (MTD for ITSA), and more broadly from April 2027.
For sole traders and landlords brought into Making Tax Digital for Income Tax Self Assessment (MTD for ITSA), the new penalty system will apply from the tax year in which they join MTD. Those outside of MTD will move to the new Self Assessment penalty system from April 2027.
The penalties for late payments will apply in two stages: a first penalty after 15 days, and then a second penalty after 30 days.
The penalty will then accrue after this date until it is paid:
Date | Penalty |
|---|
| |
| |
| 2% of the tax outstanding after day 15, plus 2% of the tax outstanding at day 30. After this date, the penalty will accrue at 4% per annum |
There will also be a points system introduced. One point will be received each time the taxpayer misses a payment date, and once the threshold has been surpassed, a fine of £200 will be applied, and then reapplied for each subsequent missed submission.
The new Self Assessment points system will work as follows:
Submission frequency | Penalty threshold |
|---|
| |
Quarterly (including MTD for ITSA) | |
| |
You can read about the proposed changes on the Gov.uk website.
Making Tax Digital and Self Assessment penalties
Making Tax Digital for Income Tax Self Assessment (MTD for ITSA) is a major reform that changes both how you report your income to HMRC and how penalties are applied. Under MTD for ITSA, sole traders and landlords will replace the traditional annual Self Assessment return with quarterly digital updates submitted via HMRC-approved software, followed by a final year-end declaration.
MTD for ITSA will apply in phases based on your qualifying income (gross income from self-employment and property combined, before expenses):
April 2026: Sole traders and landlords with qualifying income over £50,000
April 2027: Those with qualifying income over £30,000
April 2028: Those with qualifying income over £20,000 (planned)
Crucially, once you’re signed up for MTD for ITSA, the new points-based penalty system described above will apply to you for late submission of your quarterly updates and final declaration - not just for the annual return. This means you could accumulate penalty points across four submission deadlines per year rather than one. Points and penalties for MTD for ITSA are tracked separately from any VAT penalty points you may have.
For a full breakdown of how MTD penalties work - including the points thresholds, late payment rules, and how to appeal - read our dedicated guide: Making Tax Digital penalties: your guide to the new rules.
Leveraging Tide for your Self Assessment
Maintaining good control of your accounting is crucial when it comes to avoiding Self Assessment penalties.
Key information to remember:
5 October: Register for Self Assessment
31 October: File paper tax return
31 January: File online tax return
31 January: Pay your tax bill
The documents you’ll want to have on hand include:
Bank statements
P60 or any other records of income you’ve already paid taxes on (if you’re also employed)
Invoices you issued
Records of expenses relating to your small business or self-employment
Receipts of charitable contributions
Records of pensions
Tide has all the tools you need to operate your business smoothly. Our free business bank account allows you to handle all of your business transactions, and our accounting software includes free, HMRC-recognised Making Tax Digital tools, helping you keep track of everything in one place.
Photo by Pavel Danilyuk, published on Pexels
