What Happens If You Miss the Self Assessment Deadline?

Life happens. Maybe you forgot, maybe you were ill, maybe the deadline just crept up on you. Whatever the reason, missing the Self Assessment deadline isn't the end of the world — but it does come with consequences.

This guide explains exactly what happens when you miss the deadline, how much you'll owe in penalties, and what you can do right now to minimise the damage.

The Two Deadlines

There are actually two separate deadlines, and missing each has different penalties:

Deadline	What it's for	Penalty for missing
31 January	Filing your online tax return	Automatic penalties (see below)
31 January	Paying your tax bill	Interest + late payment penalties

You can miss one without missing the other. Filing late and paying late have separate penalty systems.

Late Filing Penalties

HMRC's penalty system for late filing is automatic and escalates over time.

Immediate Penalty: 1 Day Late

The moment you're one day late — even if you owe no tax — you receive an automatic £100 penalty.

This penalty applies even if:

• You're due a refund
• You owe nothing
• You're only a few hours late

Example: Sarah submitted her return at 1am on 1 February. Despite owing nothing, she received a £100 penalty.

3 Months Late: Daily Penalties

If you still haven't filed after 3 months, HMRC adds £10 per day for up to 90 days.

• Maximum: £900
• Total at 6 months: £100 + £900 = £1,000

6 Months Late: Additional Penalty

At 6 months, HMRC adds the higher of:

• £300, or
• 5% of the tax due

Example: If you owe £8,000 in tax, the 6-month penalty is £400 (5% of £8,000).

12 Months Late: Severe Penalty

At 12 months, another penalty applies — again the higher of:

• £300, or
• 5% of the tax due

In serious cases (deliberate withholding), this can rise to 100% of the tax due.

Total Potential Penalties for Late Filing

Timeframe	Penalty	Cumulative total
1 day	£100	£100
3 months	£10/day (max £900)	£1,000
6 months	£300 or 5% of tax	£1,300+
12 months	£300 or 5% of tax	£1,600+

And this is just for late filing — late payment has its own penalties.

Late Payment Penalties

If you miss the payment deadline on 31 January, a separate penalty system kicks in.

30 Days Late

5% of tax unpaid is added as a penalty.

Example: You owe £3,000 and haven't paid by 2 March → £150 penalty.

6 Months Late (31 July)

Another 5% of remaining unpaid tax is added.

Example: Still owe £3,000 by August → another £150 penalty.

12 Months Late

Yet another 5% of remaining unpaid tax.

Interest on Late Payment

On top of penalties, HMRC charges interest on all late payments. The current rate is around 7.5% per year, but this changes with Bank of England rates.

Interest is calculated daily from the due date until you pay.

Example calculation:

Amount owed	Days late	Interest rate	Interest charged
£5,000	90 days	7.5% p.a.	~£92

Interest compounds, so the longer you wait, the more you owe.

What To Do Right Now

If you've missed the deadline, act immediately. Every day matters.

Step 1: File Your Return

File as soon as possible — even if you can't pay the tax yet.

Why file first?

• Stops the daily £10 penalties from accumulating
• Prevents escalation to 6-month and 12-month penalties
• Shows HMRC you're taking action

Go to GOV.UK Self Assessment and submit your return today.

Step 2: Pay What You Can

Any payment reduces the amount subject to interest and penalties.

Payment options:

• Online banking (fastest)
• Debit card via HMRC online
• Direct Debit
• CHAPS same-day bank transfer
• At your bank (allow 3 working days)

Even if you can only pay 50%, pay it. The remaining interest is calculated on the unpaid amount only.

Step 3: Set Up Time to Pay

If you can't pay the full amount, you may be able to spread payments over monthly instalments.

Time to Pay eligibility (online):

• Tax debt up to £30,000
• All tax returns filed
• No existing payment plans
• Plan to pay within 12 months

How to set it up:

1. Go to Set up a Self Assessment payment plan
2. Enter your payment details
3. Choose monthly payment amount
4. Set up Direct Debit

For debts over £30,000, call HMRC's Payment Support Service to discuss options.

Important: Setting up a payment plan doesn't remove penalties, but it prevents further enforcement action and may reduce your stress.

Step 4: Check If You Can Appeal

You may be able to have penalties cancelled if you have a "reasonable excuse."

What counts as a reasonable excuse:

• Death of a close family member around the deadline
• Serious illness that prevented you from filing
• Fire, flood, or theft that destroyed records
• HMRC service issues (if you can prove attempted submission)
• Partner or accountant failed to submit (in some circumstances)

What doesn't count:

• "I forgot"
• "I was too busy"
• "I didn't know I had to file"
• "My accountant didn't remind me"
• "I was waiting for paperwork" (you should estimate)

How to appeal:

1. Go to Appeal a Self Assessment penalty
2. Explain your circumstances
3. Provide evidence (medical letters, death certificate, etc.)
4. HMRC will review and respond

Appeals generally have a higher success rate if you:

• Had a genuine emergency
• Filed as soon as circumstances allowed
• Have a good compliance history

Worst Case: What If You Do Nothing?

If you ignore HMRC completely, they will escalate enforcement:

Escalation timeline:

Stage	What happens
1-3 months	Penalty notices and letters
3-6 months	Demand letters, possible phone calls
6-12 months	Debt collection agencies may be used
12+ months	County Court Judgments (CCJs), bailiff visits possible

Serious consequences:

• CCJs affect your credit rating for 6 years
• Bailiffs can seize goods to cover the debt
• Bankruptcy proceedings in extreme cases
• Criminal prosecution for deliberate evasion (rare but possible)

How to Avoid This Next Year

Once you've sorted out this year's situation, take steps to prevent it happening again:

1. File early — Returns open from 6 April. The earlier you file, the sooner you know what you owe.

2. Set up payment reminders — Add 31 January to your calendar with alerts at 6 months, 3 months, 1 month, and 1 week before.

3. Save for your tax bill — Put aside 20-30% of your self-employed income as you earn it.

4. Use accounting software — Apps like FreeAgent, QuickBooks, or Xero track income/expenses and estimate your tax bill.

5. Consider an accountant — For straightforward affairs, filing yourself is fine. For anything complex, professional help may save you money and stress.

Specific Scenarios

"I filed on time but can't pay"

You'll only face late payment penalties, not late filing penalties.

Actions to take:

• Pay what you can immediately
• Set up Time to Pay for the rest
• Interest will apply from 31 January

"I didn't know I had to file"

Ignorance unfortunately isn't a reasonable excuse.

You're still liable for:

• The tax itself
• Late filing penalties
• Late payment penalties and interest

However, if it's your first offence and you act quickly, HMRC may be more lenient if you call and explain.

"I'm due a refund but filed late"

You'll still receive the refund, but you'll also get the £100 late filing penalty.

The penalty still applies even though you owe nothing.

"My accountant made an error"

You're responsible for your own tax return, even if you use an accountant.

If your accountant genuinely made an error, you may have grounds to:

• Claim against their professional indemnity insurance
• Dispute their fees
• Report them to their professional body

But HMRC will still expect you to pay penalties — your recourse is against the accountant, not HMRC.

The Bottom Line

Missing a deadline is stressful, but it's recoverable. The key points:

1. File immediately — Every day costs money
2. Pay what you can — Partial payment is better than none
3. Set up Time to Pay — If you can't pay in full
4. Appeal if you have grounds — But be realistic about success chances
5. Learn from it — Set up systems to prevent next year

The worst thing you can do is bury your head in the sand. HMRC won't forget, and the penalties will keep growing until you act.

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This guide is for informational purposes only and does not constitute tax, legal, or financial advice. Tax rules change frequently. Always verify current requirements on GOV.UK or consult a qualified accountant for your specific situation.

Official Sources

• Self Assessment penalties - GOV.UK
• If you cannot pay your tax bill on time - GOV.UK
• Appeal a Self Assessment penalty - GOV.UK
• Pay your Self Assessment tax bill - GOV.UK