HMRC charges automatic penalties for late Self Assessment returns and late tax payments. These penalties apply whether or not you owe any tax, and they accumulate quickly if left unaddressed.
The good news is that every Self Assessment penalty is avoidable if you know the deadlines and act within them. This guide explains exactly what the penalties are, how to avoid them, and what to do if you have already received one.
Self Assessment Deadlines You Must Know
| Deadline | What It Covers |
| 5 October | Register for Self Assessment if you are new (for the previous tax year) |
| 31 October | File a paper Self Assessment return for the previous tax year |
| 31 January | File your online Self Assessment return and pay all tax owed |
| 31 July | Pay your second payment on account (if applicable) |
The 31 January deadline is the most critical. It covers both the filing of your return and the payment of any tax owed, including the first payment on account toward the following year’s bill. Missing it triggers immediate penalties.
The Full Penalty Schedule for Late Filing
| How Late | Penalty |
| 1 day late (from 1 February) | £100 automatic penalty — applies even if no tax is owed |
| 3 months late (from 1 May) | £10 per day for up to 90 days — maximum additional £900 |
| 6 months late (from 1 August) | 5% of the tax owed or £300, whichever is greater |
| 12 months late (from 1 February next year) | A further 5% of tax owed or £300, whichever is greater — higher in cases of deliberate withholding |
A return that is 12 months late with a significant tax liability can generate penalties well in excess of the original tax owed. Acting quickly once you realise you have missed a deadline limits the damage significantly.
Penalties for Late Payment of Tax
Late payment of Self Assessment tax attracts separate penalties from late filing:
| How Late | Penalty |
| 30 days late | 5% of unpaid tax |
| 6 months late | A further 5% of unpaid tax |
| 12 months late | A further 5% of unpaid tax |
In addition to these penalties, HMRC charges daily interest on unpaid tax from the due date. The interest rate is set at the Bank of England base rate plus 2.5%. Interest continues to accrue until the tax is paid in full.
How to Avoid Every Self Assessment Penalty
File on time even if you cannot pay
The filing penalty and the payment penalty are separate. If you cannot afford to pay your tax bill, file the return on time anyway. This avoids the late filing penalties entirely. You can then contact HMRC to arrange a payment plan (called a Time to Pay arrangement) for the tax owed. A payment plan avoids the late payment surcharges, though interest still accrues.
Set calendar reminders for all key dates
The 31 January deadline catches many people out because it falls in the middle of January when Christmas and New Year have just passed. Set a reminder in October or November to gather your records and begin the return. Do not wait until January.
Keep records throughout the year
One of the main reasons people miss the Self Assessment deadline is that gathering records, receipts, and income figures takes longer than expected. Maintaining a simple income and expense record throughout the year means everything is ready when it is time to file.
Use an accountant
An accountant’s primary function in the Self Assessment process is to make sure your return is filed on time and accurately. A missed deadline is rarely the fault of clients who use an accountant. If you find Self Assessment stressful or difficult to manage yourself, using an accountant is the most reliable way to avoid penalties.
Register on time if you are new to Self Assessment
If you have a new source of untaxed income, such as rental income, self-employment income, or dividends above your allowance, you must register for Self Assessment by 5 October following the end of the tax year in which you received that income. Missing the registration deadline adds to the complexity and can lead to a late filing penalty on top.
What to Do if You Have Already Missed the Deadline
Step 1. File immediately. Every day you delay adds to the daily penalty if you are already more than three months late. File the return as soon as possible regardless of whether you can pay the tax.
Step 2. Pay what you can. If you cannot pay the full amount, pay as much as you can immediately. Late payment penalties and interest are calculated on the amount outstanding. Reducing the outstanding balance reduces the penalty and interest that accumulates.
Step 3. Contact HMRC about a payment plan. HMRC’s Time to Pay service allows you to spread payments over a period of time. You can set up a payment plan online if you owe less than £30,000 and are less than 60 days past the deadline. For larger amounts or older debts, call HMRC directly.
Step 4. Consider appealing the penalty. If you have a reasonable excuse for missing the deadline, you can appeal the late filing penalty. HMRC accepts genuine emergencies and exceptional circumstances as reasonable excuses.
What Counts as a Reasonable Excuse?
HMRC accepts appeals against late filing penalties when there is a genuine reasonable excuse. Examples HMRC has accepted include:
- Serious illness of the taxpayer or a close family member that prevented filing
- Bereavement of a close family member shortly before the deadline
- Technical failures with HMRC’s own online filing system
- Postal delays for paper returns sent in good time
- A natural disaster or fire that destroyed records
HMRC does not accept the following as reasonable excuses:
- Not receiving a reminder from HMRC
- Not understanding that you needed to file a return
- Finding the online system difficult to use
- Pressure of work or being too busy
- Your accountant making an error (though you may have a separate claim against your accountant)
If you believe you have a reasonable excuse, submit your appeal in writing to HMRC as soon as possible after the penalty is issued. Include all supporting evidence.
| Penalty appeals: act quickly There is a 30-day window to appeal a Self Assessment penalty from the date it is issued. Missing the appeal deadline significantly reduces your chances of success. If you receive a penalty notice and believe you have grounds to appeal, act within that 30-day window. |
Payments on Account: A Common Surprise
Many people receive unexpected penalty notices not because their return was late but because they missed a payment on account deadline. Payments on account are advance payments toward your next year’s tax bill.
If your Self Assessment tax bill exceeds £1,000, HMRC requires two payments on account:
- First payment on account: 31 January (same day as your current year’s tax payment)
- Second payment on account: 31 July
Each payment is 50% of your previous year’s tax bill. In your first year of significant Self Assessment tax, your January bill can be up to 150% of the tax you owe for that year. Not budgeting for this is one of the most common causes of cash flow problems for self-employed people and landlords.
Frequently Asked Questions
What is the penalty for filing Self Assessment one day late?
A £100 automatic penalty applies from the first day after the deadline, even if no tax is owed and even if you have a good reason for the delay. The only way to avoid this penalty after the deadline has passed is to successfully appeal it on the grounds of a reasonable excuse.
Can HMRC waive a Self Assessment penalty?
Yes, if you have a reasonable excuse. You must appeal the penalty in writing within 30 days of the date it was issued, explaining your circumstances and providing supporting evidence. HMRC considers each appeal on its merits.
What happens if I cannot pay my Self Assessment tax bill?
File the return on time regardless of whether you can pay. Then contact HMRC to set up a Time to Pay arrangement. This allows you to pay in instalments over an agreed period. Interest still accrues on the unpaid amount, but the late payment surcharges are avoided if you stick to the agreed plan.
Do I get a penalty if I file early?
No. You can file your Self Assessment return any time after the end of the tax year, which is 6 April. Filing early has no downside and is recommended if you want to know your tax bill in advance and plan for the payment.
Will HMRC remind me about the Self Assessment deadline?
HMRC sends reminders but does not guarantee you will receive them. Not receiving a reminder from HMRC is not accepted as a reasonable excuse for missing the deadline. You are responsible for knowing and meeting the deadlines regardless of whether you receive a reminder.
Never Miss a Self Assessment Deadline Again
M&B Tax Services files Self Assessment returns for individuals, self-employed people, landlords, and limited company directors across the UK. We manage deadlines, chase information from clients in good time, and make sure returns are filed and tax is paid on time every year.
We are ICB-regulated accountants based in Rugby. If you have received a penalty or are worried about a missed deadline, we can advise on your options and help you resolve it with HMRC.
Book a free 30-minute call and we will review your Self Assessment position at no cost.
Joanna Bruty
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