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What Happens If You File Late? A Guide to HMRC Penalties and Mitigation

Missed the January 31st deadline? Discover what happens next, how much you'll be fined, and the specific steps you can take to stop the damage today.

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TaxWiz Editorial

Tax Content Writer • Modified 2026-04-08

The Immediate Damage

If it is February 1st and you haven't hit "Submit," you probably have a knot in your stomach. Here is exactly what is happening in the HMRC computer system right now.

The Short Answer

You've been automatically fined £100.

This fine applies even if you owe £0 in tax. If you missed the deadline by even one minute, a £100 penalty is automatically issued against your UTR. This is just the beginning.

The Escalation Timeline:

  • 1 Day Late: £100 automatic penalty.
  • 3 Months Late: Daily penalties of £10 for up to 90 days (Max £900).
  • 6 Months Late: Greater of £300 or 5% of the tax due.
  • 12 Months Late: Greater of £300 or 5% of the tax due (sometimes 100% of the tax due).

Damage Control: Do This Now

The most important thing you can do is stop the clock. The penalties for being 3 months late are far more aggressive than the initial £100 fine.

Action Plan: Stopping the Fines

  1. File your return immediately: Don't wait to find a 'better' accountant or till you have the money to pay. Filing stops the 'late filing' clock.
  2. Estimate if you have to: If you are missing one or two receipts, estimate the figure using an 'Estimated' flag on your return. This is better than filing late.
  3. Pay whatever you can: If you can't pay the full bill, pay what is in your bank account right now. This reduces the interest charges.
Go to HMRC Portal

Reasonable Excuses

HMRC will often waive penalties if you have a "Reasonable Excuse." These are usually events that were out of your control.

HMRC usually accepts:

  • Family Bereavement: A close family member passing away around the deadline.
  • Serious Illness: An unexpected hospital stay that prevented you from filing.
  • Technical Failure: A confirmed crash on the HMRC website (you will need a screenshot).
  • Service Delays: Mail strikes or postal delays (if you can prove them).

HMRC will NOT accept:

  • "I forgot the date."
  • "My accountant let me down."
  • "The HMRC website was too difficult to use."
  • "I didn't have enough money in my account."

How to Appeal a Fine

If you believe you have a reasonable excuse, you have 30 days from the date of the penalty notice to appeal.

Avoid These Appeal Mistakes
  • Don't appeal before you file: HMRC will ignore an appeal for a return that still hasn't been submitted.
  • Don't ignore the letter: If you don't appeal within 30 days, it becomes a legal debt that is much harder to challenge later.
  • Don't provide vague details: If you were ill, provide the hospital dates or a doctor's note reference number.

Your Next Step

If you haven't even registered yet, you need to do that before you can even begin to file.

While You Wait...

  1. Follow our [How to Register] guide to get your UTR number immediately.
  2. Check our [UTR Number Guide] to see if you already have one and just forgot it.
  3. Once your number arrives, use our [Allowable Expenses Guide] to lower your final bill.
Registration Guide

Frequently Asked Questions

HMRC may cancel a fine if you have a 'reasonable excuse' for filing late, but usually, 'lack of funds' is not considered an excuse. They are more likely to set up a payment plan for the tax itself.
No. HMRC does not report late tax returns or late payments to credit agencies like Experian or Equifax. However, it can affect your ability to get a mortgage if the lender asks for your SA302 forms.
Unfortunately, you will still get the £100 fine. However, you should file as soon as the UTR arrives. You can then appeal the fine based on the delay in receiving your number if the delay was on HMRC's end.

Tax Disclaimer: TaxWiz provides general educational information and guides for UK residents. While we strive to maintain accuracy for the 2026/27 tax year, tax rules are subject to change. This content does not constitute regulated financial, legal, or tax advice. For complex situations, we strongly recommend consulting a qualified UK accountant. View our full Disclaimer.