Submitting a Self Assessment tax return late can result in automatic penalties, interest, and increased scrutiny from HMRC. Whether you are self-employed, a landlord, a company director, or earn untaxed income, meeting HMRC deadlines is critical. This guide explains exactly what happens if your Self Assessment Tax Return is late, how penalties are calculated, and what you should do if you have already missed the deadline.
1. Key Self Assessment Deadlines
To avoid penalties, you must meet the following annual deadlines:
- 31 January – Filing deadline for online returns.
- 31 January – Deadline to pay balancing tax payment and first payment on account (if applicable).
- 31 July – Deadline for second payment on account.
Missing any of these deadlines triggers penalties or interest.
2. What Happens If You File Your Self Assessment Late?
HMRC applies penalties based on how late your filing is. These penalties apply even if you have no tax to pay.
A) 1 Day Late: £100 Penalty
As soon as the deadline passes, HMRC issues a fixed £100 late filing penalty.
This applies regardless of how much tax you owe or even if no tax is due.
B) 3 Months Late: Daily Penalties
If your tax return is still outstanding after three months, HMRC adds:
- £10 per day for up to 90 days
- Maximum daily penalty total: £900
For example, if you file on 1 May, you could face the full £900 daily penalty charge.
C) 6 Months Late: Additional Penalty
At six months overdue, HMRC charges the higher of:
- £300, or
- 5% of the tax due
This is added on top of earlier penalties.
D) 12 Months Late: Further Penalty
After 12 months, HMRC applies another penalty:
- £300, or
- 5% of the tax due
In serious cases, such as deliberate tax concealment, HMRC can increase the penalty up to 100% of the tax owed.
3. Can HMRC Cancel Penalties? (Reasonable Excuse)
HMRC may consider cancelling or reducing penalties if you have a reasonable excuse. A reasonable excuse means something unexpected prevented you from filing or paying on time.
Accepted Reasons
- A serious illness or hospitalisation
- Bereavement of a close family member
- Fire, flood, or natural disaster
- HMRC online service issues
- Unexpected technical failures
Reasons Not Accepted
- Forgetting the deadline
- Accountant delays or errors
- Lack of understanding of tax rules
- Not receiving reminders
You can appeal online through your HMRC Self Assessment account.
4. What To Do If You Have Already Missed the Deadline
If you have missed the deadline, taking immediate action can help reduce how much you owe.
1. File the return as soon as possible
Every day you delay increases your penalties.
2. Pay as much as you can immediately
This reduces interest and future late-payment penalties.
3. Set up a Time to Pay arrangement
HMRC may allow you to pay your tax in monthly instalments if you cannot afford the full amount.
4. Gather accurate records
Ensure your figures are correct before filing to avoid amendments later.
5. Contact HMRC if circumstances prevented filing
You may be eligible for a penalty appeal.
How to Avoid Late Self Assessment Penalties in the Future?
- Keep business and personal records up to date throughout the year.
- Use accounting or bookkeeping software to track income and expenses.
- File your tax return early, ideally soon after the tax year ends on 6 April.
- Set reminders for the 31 January and 31 July deadlines.
- Work with an accountant to prepare your return in advance.
FAQs (Frequently Asked Questions)
1. What happens if I file my Self Assessment late?
If you file late, HMRC automatically charges a £100 penalty. If the return is still outstanding after 3 months, daily penalties apply (£10 per day, up to £900). At 6 and 12 months late, further penalties of £300 or 5% of the tax due (whichever is higher) are added. Interest and late-payment penalties apply separately if tax remains unpaid.
2. How do I avoid late Self Assessment penalties?
You can avoid penalties by filing your tax return before the 31 January deadline, keeping accurate records throughout the year, using accounting software, setting reminders, filing early (from 6 April onward), and working with an accountant. Submitting your return well before the deadline is the most reliable way to avoid penalties.
3. Can I get an extension on my Self Assessment?
HMRC rarely grants deadline extensions. Extensions are only considered in exceptional cases, such as severe illness, bereavement, or technical failures on HMRC’s side. These fall under “reasonable excuse” rather than a formal extension. In normal circumstances, you must file by the standard deadline.
4. How long does a Self Assessment tax return take?
It depends on your situation. A simple return with PAYE income and small amounts of untaxed income can take less than an hour. More complex returns involving self-employment, rental income, capital gains, or foreign income may take several hours. Filing early gives time to organise records and avoid errors.
5. How much is the late fee for Self Assessment?
The initial late filing fee is £100. Additional penalties apply at 3 months (daily penalties), 6 months (5% or £300), and 12 months (5% or £300). Late payment penalties are separate and start at 5% of unpaid tax after 30 days.
6. What is the deadline for Self Assessment?
The main deadline for online Self Assessment tax returns is 31 January following the end of the tax year. This is also the deadline to pay the balancing payment and the first payment on account. The second payment on account is due on 31 July.
Final Thought
Filing your Self Assessment on time is the simplest way to avoid penalties and interest. If you need help filing your Self Assessment on time or want an expert to handle your tax returns, our team can manage the entire process for you accurately, efficiently, and before the deadline. Get in touch today for reliable, stress-free tax support.