HMRC Late Filing Penalties for Self Assessment 2026/27: How Much Will You Pay?

Missing the Self Assessment deadline is an expensive mistake that many UK taxpayers make each year. HMRC's penalty regime is automatic and escalating -- the longer you leave it, the more you owe. Here is exactly what the penalties are for 2026/27 returns and what you can do to avoid or challenge them.

Key Deadlines for the 2025/26 Tax Year

• 5 April 2026: End of the 2025/26 tax year
• 31 October 2026: Paper return deadline
• 31 January 2027: Online return and payment deadline
• 31 July 2027: Second payment on account (if applicable)

Most people file online, so the relevant deadline is 31 January 2027 for the 2025/26 return.

For the 2026/27 tax year, the online filing deadline will be 31 January 2028.

The Penalty Structure

HMRC's automatic penalty regime works in stages:

Day 1 -- Immediate Penalty

A flat £100 penalty applies the moment the return is late, regardless of whether you owe any tax or have already paid everything you owe. If your tax bill is zero, you still get the £100 fine.

After 3 Months -- Daily Penalties

If the return is still outstanding after 3 months (approximately 30 April for a January deadline), HMRC adds £10 per day, up to a maximum of 90 days. This means up to £900 in daily penalties on top of the initial £100.

Total possible after 3 months + 90 days: £1,000

After 6 Months -- Tax-Based Penalty

At the 6-month mark, HMRC charges a further penalty of either:

• 5% of the tax due, or
• £300 -- whichever is greater

If you owe £10,000 in tax, this adds £500. If you owe £1,000, it adds £300 (minimum applies).

After 12 Months -- Second Tax-Based Penalty

At 12 months late, another penalty of 5% of the tax due (minimum £300) is charged. In cases where HMRC determines you deliberately withheld information, this can rise to:

• 70% of the tax due for deliberate but not concealed failure
• 100% of the tax due for deliberate and concealed failure
• Up to 200% for offshore non-compliance

Summary Table

Maximum automatic penalties for an average return with moderate tax due: well over £1,600 before interest.

Interest on Late Payment

Separate from filing penalties, HMRC charges interest on any tax paid late. The rate in 2026/27 is 7.5% per annum (Bank of England base rate plus 2.5 percentage points).

Interest accrues from the payment due date (31 January for the balancing payment) to the date you actually pay. On a £5,000 bill paid six months late, that is roughly £187.50 in interest charges alone.

Interest and penalties are separate charges. You can receive both.

How to Avoid Penalties

File on time even if you cannot pay. The filing penalty and the payment penalty are separate. If you file on 31 January but cannot pay the full amount, you avoid all filing penalties. You will pay interest on the late payment, but avoiding the £100+ daily penalties is worthwhile.

Register for Self Assessment early. HMRC needs time to issue your Unique Taxpayer Reference (UTR). New registrations can take up to 10 working days. Register at least by October for a January deadline.

Use HMRC's Time to Pay. If you cannot pay your bill in full, contact HMRC before the deadline. A Time to Pay arrangement lets you spread payments over time -- you still pay interest, but you avoid surcharges and formal debt recovery action.

Keep records. Good records mean you can file quickly and accurately. Scrambling for bank statements and receipts in January is the main reason people miss deadlines.

Reasonable Excuse

HMRC can cancel or reduce a penalty if you have a reasonable excuse for late filing. Accepted excuses include:

• Unexpected serious illness or hospitalisation
• Death of a close family member just before the deadline
• IT failure on HMRC's systems (HMRC publishes these)
• Postal delays for paper returns

Not accepted: forgetting, not knowing the deadline, being too busy, or assuming an accountant had filed on your behalf without checking.

You must appeal within 30 days of the penalty notice. Appeals are made via HMRC's penalty appeal form or directly in your online account.

Deliberate Non-Filing

If HMRC believes you are deliberately avoiding filing -- rather than simply being late -- penalties escalate sharply and the possibility of investigation increases. HMRC's Connect system cross-references employment records, bank data, land registry, and PAYE data to identify likely non-filers.

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Use our Income Tax Calculator to estimate what you owe before filing, so there are no surprises when you submit your Self Assessment return.