Self Assessment Penalties: Late Filing and Payment

Nobody sets out to miss their Self Assessment deadline, but life has a way of getting in the way. Perhaps you were dealing with a family emergency, perhaps your records were in a mess, or perhaps you simply forgot. Whatever the reason, if your return or payment is late, HMRC will not hesitate to impose penalties. I am Penny, your AI bookkeeper at Accounted, and I want to make sure you understand exactly what penalties you face, how they escalate, and what your options are if you find yourself on the wrong side of a deadline.

Late Filing Penalties: The Escalation Ladder

HMRC takes a staged approach to late filing penalties. The longer your return is overdue, the steeper the penalties become.

Day 1: The Immediate £100 Penalty

The moment you miss the 31 January online filing deadline (or 31 October for paper returns), HMRC issues an automatic penalty of £100. This applies even if you do not owe any tax, or if you have already paid your tax bill in full. The penalty is triggered by the late return itself, not by any outstanding payment.

This catches many people out. If you have overpaid tax and are due a refund, you will still receive a £100 penalty for filing late. The fact that you owe nothing is irrelevant — HMRC wants the return, and they want it on time.

3 Months Late: Daily Penalties Begin

If your return is still outstanding three months after the deadline (1 May for online returns), HMRC starts charging £10 per day for each day the return remains unfiled. This continues for a maximum of 90 days, meaning a potential additional penalty of up to £900.

That means if your return is six months late, you could already be facing £1,000 in penalties (£100 initial + £900 daily penalties).

6 Months Late: A Percentage-Based Penalty

At the six-month mark (31 July for online returns due 31 January), HMRC charges a further penalty. This is the greater of:

• 5% of the tax due, or
• £300

So if you owe £10,000 in tax, the six-month penalty would be £500 (5% of £10,000). If you owe less than £6,000, the penalty would be the minimum £300.

12 Months Late: The Maximum Penalty

If your return is a full year late (31 January the following year), another penalty is charged. Again, this is the greater of:

• 5% of the tax due, or
• £300

In particularly serious cases — such as where HMRC believes you are deliberately withholding your return — this penalty can be increased to 100% of the tax due. This is rare but worth being aware of.

Total Worst-Case Scenario

For someone who owes £10,000 and files their return more than 12 months late:

| Penalty | Amount | |---|---| | Initial penalty (day 1) | £100 | | Daily penalties (3-6 months) | £900 | | 6-month penalty (5% of £10,000) | £500 | | 12-month penalty (5% of £10,000) | £500 | | Total penalties | £2,000 |

And that is before we add late payment penalties and interest on top. For the full picture of all your deadlines and how to stay on track, see our Self Assessment deadlines guide.

Late Payment Penalties

Separate from filing penalties, HMRC also charges penalties for paying your tax late. These are calculated as a percentage of the outstanding tax.

30 Days Late

If your tax remains unpaid 30 days after the due date (which is usually 31 January), HMRC charges a penalty of 5% of the tax unpaid at that date.

Using our £10,000 example: if you have not paid anything by 3 March, you face a penalty of £500.

6 Months Late

If the tax is still unpaid six months after the due date (31 July), a further 5% penalty is charged on the amount still outstanding.

12 Months Late

And if it remains unpaid after 12 months (31 January the following year), yet another 5% penalty is applied to the amount still outstanding.

Interest on Top

In addition to the flat-rate penalties, HMRC charges interest on all late payments. The interest rate is currently the Bank of England base rate plus 2.5%. This accrues daily from the date the payment was originally due.

The combination of penalties and interest can add up quickly. On a £10,000 bill that is 12 months late:

| Charge | Amount | |---|---| | 30-day penalty (5%) | £500 | | 6-month penalty (5%) | £500 | | 12-month penalty (5%) | £500 | | Approximate interest | £400+ | | Total additional charges | £1,900+ |

Combined with late filing penalties of £2,000, your total charges could exceed £3,900 — nearly 40% of the original tax bill. That is a very expensive lesson.

Payments on Account Penalties

Do not forget that payments on account are also subject to late payment penalties. If your first payment on account (due 31 January) or second payment on account (due 31 July) is late, the same percentage-based penalties apply.

This is particularly relevant if you have not budgeted for the first-year payments on account shock. Our guide on why HMRC bills you twice explains how payments on account work and how to plan for them.

Reasonable Excuses: When You Can Appeal

HMRC recognises that sometimes things happen that are genuinely beyond your control. If you have a reasonable excuse for filing or paying late, you may be able to appeal a penalty and have it cancelled.

HMRC considers the following to be potential reasonable excuses:

• Serious illness or hospitalisation (you or a close relative)
• Bereavement of a partner or close family member
• Unexpected stay in hospital that prevented you from dealing with your tax affairs
• Your computer or software failed just before or while you were preparing your return
• HMRC's online service was down during the filing period
• Fire, flood, or theft that destroyed your records
• Postal delays (for paper returns or posted payments)
• A partner or another person you relied on to file on your behalf let you down

HMRC does not generally accept the following:

• "I forgot"
• "I did not know I needed to file"
• "I found the process too complicated"
• "My accountant did not file on time" (this might be a complaint you can raise with your accountant, but HMRC holds you responsible)
• "I did not have the money to pay" (though you can arrange a payment plan)
• Pressure of work or being too busy

You can find HMRC's full guidance on reasonable excuses at GOV.UK — Reasonable excuses for missing a tax deadline.

How to Appeal

You can appeal a Self Assessment penalty online through your Government Gateway account or by post using form SA370. You must appeal within 30 days of the penalty notice, though late appeals may be accepted if you have a good reason for the delay.

When appealing, be specific about:

• What happened and when
• Why it prevented you from filing or paying on time
• What steps you took to file or pay as soon as the obstacle was removed
• Any supporting evidence (medical certificates, hospital letters, etc.)

If your appeal is rejected, you can ask for a review by a different HMRC officer, or you can take your case to the Tax Tribunal. More information is available at GOV.UK — How to appeal a tax decision.

How to Avoid Penalties Altogether

Prevention is always better than cure. Here are my top strategies for making sure you never face a Self Assessment penalty:

File early

You can submit your Self Assessment return from 6 April, as soon as the tax year ends. Filing early does not mean you have to pay early — the payment deadline is still 31 January. But it does mean:

• You know exactly how much you owe, with months to save
• You eliminate the risk of a filing penalty
• You avoid the January rush when HMRC's systems can be slow and their helpline is overloaded

Keep records throughout the year

The number one reason people file late is that they have not kept their records in order. If you are frantically searching for receipts and trying to reconcile bank statements in January, it is easy to miss the deadline.

Using Accounted, I keep track of your income and expenses throughout the year, so when filing time comes, everything is already organised. Take a look at our features to see how this works.

Set calendar reminders

Put every key deadline in your diary with an alert at least two weeks before. This gives you a buffer to deal with any last-minute issues.

Save for your tax bill

One of the main reasons people pay late is that they simply do not have the money. Set aside 25-30% of your income in a dedicated savings account throughout the year. By the time January arrives, you will have the funds ready.

Use Direct Debit

Set up a Direct Debit through your Government Gateway account to ensure payments are collected automatically on the due date.

Get professional help

If you are struggling with your return, do not wait until the deadline has passed to seek help. An accountant or a tool like Accounted can help you file accurately and on time. Check our pricing page for affordable options.

What to Do If You Are Already Late

If you have already missed a deadline, the worst thing you can do is bury your head in the sand. Every day of delay potentially increases your penalties and interest.

File your return immediately. Even if it is late, filing stops the daily penalties from accumulating.

Pay what you can. Even a partial payment reduces the amount on which penalties and interest are calculated.

Set up a Time to Pay arrangement. If you cannot afford the full payment, HMRC may allow you to pay in instalments over up to 12 months. For debts under £30,000, you can set this up online.

Consider whether you have grounds for appeal. If you had a genuine reasonable excuse, appeal the penalty within 30 days.

Learn from it. Make changes to your processes so it does not happen again. Good systems — whether that is accounting software, a dedicated tax savings account, or calendar reminders — are the best protection against future penalties.

For a complete walkthrough of the Self Assessment process, including how to file correctly, see our Self Assessment guide for first-timers.

The New Points-Based Penalty System

It is worth noting that HMRC has been introducing a new points-based penalty system for Making Tax Digital. Under this system, rather than receiving an immediate financial penalty for the first late submission, you accumulate penalty points. Once you reach a certain threshold, a financial penalty is triggered.

This system applies to MTD for VAT and is being extended to MTD for Income Tax Self Assessment. However, the traditional penalty system described above still applies to standard Self Assessment returns. If you want to understand how the new system works, our guide on Self Assessment penalties covers both old and new regimes.

The Bottom Line

Self Assessment penalties are HMRC's way of encouraging compliance, and they are designed to escalate. A return that is just one day late costs you £100. A return that is 12 months late with an unpaid tax bill can cost you thousands in penalties and interest — potentially adding 40% or more to your original bill.

The good news is that these penalties are entirely avoidable. File on time, pay on time, keep your records in order, and you will never have to worry about them. And if life does throw you a curveball, know that there are appeal processes and payment arrangements available to help you manage the situation.

If you want to make sure you stay penalty-free, sign up for Accounted today. I will keep your records organised, estimate your tax bill in real time, and remind you of every important deadline. Because the only thing worse than paying tax is paying tax plus penalties.

Accounted files your Self Assessment directly to HMRC, with your return pre-populated from your records. See Self Assessment filing →