UK Appeal an HMRC Tax Penalty 2026/27: Reasonable Excuse, Deadlines and the Tribunal

Penalties You Can Appeal

Most HMRC penalties carry a right of appeal. The common Self Assessment penalties are:

• Late filing: GBP 100 at one day late; GBP 10/day from three months late (up to GBP 900); the greater of GBP 300 or 5% of tax at 6 and 12 months.
• Late payment: broadly 5% of unpaid tax at 30 days, 6 months and 12 months, plus daily interest from the due date.
• Failure to notify: for not registering for tax on time, based on the tax at stake.
• Inaccuracy penalties: for errors in a return, varying with whether the error was careless or deliberate.

Each notice explains the penalty and how to appeal it. The reasonable excuse route applies mainly to late filing, late payment and failure to notify.

The 30-Day Deadline

You normally have 30 days from the date on the penalty notice to appeal. The clock runs from the notice date, not the date you opened the letter, so do not delay.

Miss the window and you can still request a late appeal, but you must explain why it was late and HMRC decides whether to accept it. A strong, well-evidenced reason for the delay improves your chances.

What Counts as Reasonable Excuse

A reasonable excuse is something that prevented you meeting the deadline despite taking reasonable care. Examples that have been accepted include:

• Serious illness or a hospital stay around the deadline.
• Bereavement of a close family member shortly before the deadline.
• A fire, flood or theft that destroyed your records.
• An extended failure of HMRC online services.
• Postal or service delays genuinely beyond your control.

Crucially, once the excuse ends you must put matters right without unreasonable delay - filing or paying as soon as you reasonably can - or the excuse may not hold.

What HMRC Rejects

HMRC usually rejects excuses such as: the return was too difficult; you did not get a reminder; you relied on an agent without checking; you forgot; or pressure of work got in the way. Inability to pay is generally not a reasonable excuse for late payment, unless caused by events genuinely outside your control.

If your real problem is affordability rather than excuse, a Time to Pay arrangement is usually the better route, as it can prevent further late payment penalties building up.

How to Appeal

For Self Assessment late filing penalties you can appeal online through your account or by sending form SA370. For other penalties, follow the appeal instructions on the notice. In your appeal:

• State which penalty you are appealing and the notice date.
• Set out your reasonable excuse clearly and factually.
• Explain that you put things right as soon as the excuse ended.
• Attach evidence - medical letters, death certificates, insurance or crime reports.

Keep it concise and chronological. A clear timeline that links the excuse to the missed deadline is far more persuasive than general statements.

The HMRC Internal Review

If HMRC rejects your appeal, it offers an independent internal review by an officer not previously involved. You normally have 30 days to accept. The review is free, the officer looks at the case afresh, and a decision usually follows within about 45 days.

A review does not use up your right to go to tribunal - if you disagree with the conclusion, you then have 30 days to appeal to the First-tier Tribunal. Because a fresh reviewer sometimes overturns the original decision, a review is often worth taking.

The First-tier Tribunal

The First-tier Tribunal (Tax Chamber) is independent of HMRC. You can go there instead of, or after, an internal review. There is normally no fee. Many penalty appeals are decided on paper; others have a short hearing where you present your excuse and evidence.

The tribunal can cancel, reduce or confirm the penalty and is not bound by HMRC's internal guidance. Well-evidenced reasonable excuse arguments that HMRC rejected are sometimes accepted there, which is why the tribunal stage is a genuine and worthwhile safeguard.

Worked Examples

Example 1 - hospital stay. Maria was admitted to hospital for three weeks over late January and filed her return on 15 February, two weeks late, incurring a GBP 100 penalty.

• Penalty charged: GBP 100 fixed late filing penalty
• Excuse: serious illness preventing filing around the deadline
• Action: filed within two weeks of discharge (no unreasonable delay)
• Evidence: hospital admission and discharge letters attached to the SA370
• Outcome: reasonable excuse accepted, GBP 100 penalty cancelled

The clear timeline linking the illness to the missed deadline, plus prompt filing on recovery, made the case strong.

Example 2 - late payment, no excuse. Ben filed on time but could not pay GBP 4,000 of tax due to a cash-flow squeeze with no external cause. A 30-day late payment penalty of GBP 200 (5% of GBP 4,000) was charged.

• Penalty: GBP 4,000 x 5% = GBP 200, plus daily interest from 1 February
• Affordability alone is not a reasonable excuse, so an appeal would likely fail
• Better route: agree a Time to Pay arrangement to spread the GBP 4,000
• Time to Pay can stop further late payment penalties accruing

Ben drops the appeal and sets up a Time to Pay plan instead, limiting further penalties while he clears the balance.