A missed Self Assessment deadline calls for immediate action. Identify which return or payment is late, provide any missing information and deal with any unpaid tax.
Penalties for filing late and paying late are separate. If you do not agree with a penalty, follow the steps to appeal; however, the overdue obligation remains in place during the appeal.
Identify the deadline you missed and the tax year it relates to. Registration, filing and payment are separate requirements and may each need a different response.
The usual paper filing deadline for the 2025/26 tax year was 31 October 2026. Online filing and payment are normally due by 31 January 2027.
The 2026/27 online return is normally due by 31 January 2028. A deadline arising in 2026/27 could therefore relate to a previous tax year.
Read the GOV.UK guidance on Self Assessment penalties for the current rules.
External link: https://www.gov.uk/self-assessment-tax-returns/penalties
Check your HMRC account and any letters for:
If you missed the paper deadline, check the online deadline to see whether you can file electronically. Do not assume that a late paper return will be accepted.
If you do not think a notice is correct or necessary, ask HMRC to confirm or cancel it. Do not ignore it.
Our guide to who has to file a Self Assessment tax return explains common reporting situations.
Internal link: https://www.selfassessmentassistance.uk/blog/who-has-to-file-a-self-assessment-tax-return
Under the traditional Self Assessment penalty system, the longer a required return remains outstanding, the higher the charge. A late filing penalty can apply even if little or no tax is due.
The usual timeline is:
These charges can add up. Filing the return promptly helps prevent further filing penalties.
Read the HMRC Self Assessment penalties guidance for the standard process.
External link: https://www.gov.uk/self-assessment-tax-returns/penalties
Once you join Making Tax Digital for Income Tax, a different penalty system may apply. Do not assume that the obligations are the same as the traditional timeline.
For example, if someone must join from April 2026, the general penalty position for their 2025/26 return, payable in January 2027, remains unchanged.
This is set out in HMRC's guidance on penalties for Making Tax Digital. Check the relevant regime before estimating a charge.
Check the relevant regime before estimating a charge.
Filing your return does not pay the bill. Late filing and late payment are separate issues, as is paying tax without filing the return.
Late payment penalties are normally charged at 5% of the relevant unpaid tax at 30 days, six months and 12 months. Interest also accrues on unpaid tax; it does not replace penalties, and paying before a penalty point does not remove interest already due.
For example, an unpaid balancing payment of £2,000 after the first penalty point may generate a £100 late payment penalty, as well as interest. Additional penalties may apply on top of any filing penalties.
Check the calculation and payment breakdown in your HMRC account. The balance may be affected by payments on account and other liabilities.
Our guide to how to check your Self Assessment tax bill explains the main figures.
Internal link: https://www.selfassessmentassistance.uk/blog/how-to-check-your-self-assessment-tax-bill
If you cannot pay the full amount, HMRC may be able to help you arrange payment by the deadline through Time to Pay. Approval depends on your circumstances, and interest usually continues to accrue on tax owed.
Submit the return even if you have a payment plan.
Complete the outstanding work in order and track what has been submitted and paid. Waiting until every concern is resolved can allow further issues to arise.
Gather business income, expenses, employment records and details of other reportable income. Identify missing records quickly and request replacements where needed.
Separate the current year's transactions from those belonging to the relevant tax year. Mixing periods can create errors that require later corrections.
Our guide on how to keep Self Assessment records online explains how to organise digital records.
Internal link: https://www.selfassessmentassistance.uk/blog/how-to-keep-self-assessment-records-online
Follow the correct filing route and check the figures before submitting. Our guide to how to complete a Self Assessment tax return outlines the main preparation steps.
If information is unavailable, seek advice on whether and how to use provisional figures. Avoid guesses or unsupported estimates.
Keep the submitted return, calculation and acknowledgement. Saving a draft does not mean HMRC has received the completed return.
Check your account again after processing and review any unusual balance.
If you need to amend an error, read our guide on how to correct a Self Assessment tax return.
Internal link: https://www.selfassessmentassistance.uk/blog/how-to-correct-a-self-assessment-tax-return
Pay what you can using the correct reference and seek support for any remaining balance. Keep copies of payment confirmations and notes of discussions with HMRC.
If you need help organising outstanding work, Self Assessment filing support can help you prepare the information required.
Internal link: https://www.selfassessmentassistance.uk/
You can challenge a penalty if you believe it is incorrect or you had a reasonable excuse. Explain the circumstances, their effect and what you did once you were able to act.
Examples may include serious illness, unexpected hospital admission, bereavement or a relevant technical failure. HMRC considers each case individually and does not treat every example as an automatic excuse.
To appeal an HMRC penalty, prepare:
Follow the deadline and process stated in the notice. Appeals are often required within 30 days, and a late appeal will also need an explanation.
Not receiving a reminder is not normally accepted as a reasonable excuse. Neither is a failed payment caused by insufficient funds.
Keep a copy of the appeal. Do not assume that an appeal stops collection, interest or other obligations; check the status of your case.
Yes. Under the traditional Self Assessment system, an initial late filing penalty can apply even where no tax is due or the tax due has already been paid.
Once you have confirmed that a return is required and that the notice is accurate, decide how to respond.
No. File the required return on time and deal with payment separately. Delaying filing does not solve a payment issue and can create an additional filing penalty.
Keep communicating with HMRC about what you can afford and whether an instalment arrangement is available.
No. An accountant can review the notice, help prepare the relevant information and support an appeal where there are grounds.
Cancellation depends on the facts and HMRC's decision. Be cautious of guarantees of removal and provide a full, accurate explanation of the delay.