HMRC Penalties for Late Filing and Late Payment: What You'll Actually Owe

Most people assume that if they don't owe much tax, missing a filing deadline won't matter much. That assumption is wrong. The £100 late filing penalty applies even if you owe nothing at all — and it accumulates quickly from there. Understanding exactly what HMRC charges for late filing and late payment is the most direct motivation to stay on top of deadlines.

Late filing penalties: the four stages

Self Assessment penalties for late filing are imposed automatically once you miss the 31 January deadline. They escalate in four stages.

Stage 1 — Immediate: £100

From 1 February (the day after the 31 January deadline), a £100 fixed penalty applies. This is automatic and applies regardless of whether you owe any tax. HMRC does not issue a warning — the penalty is imposed the moment the deadline passes. It applies whether your late period is one day or one year, until the next stage triggers.

Stage 2 — Three months late: £10 per day

If the return remains unfiled three months after the original deadline (i.e., from 1 May), HMRC charges £10 per day for up to 90 days. The maximum additional penalty under this stage is £900. Combined with the initial £100, the total reaches £1,000 if you file exactly six months late.

This daily charge is applied by HMRC after reviewing late returns — it isn't always assessed automatically in real time, but it will appear on your penalty notice when you eventually file.

Stage 3 — Six months late: 5% of tax owed

If the return is still unfiled six months after the deadline (from 1 August), a further penalty of 5% of the tax owed is charged (or £300, whichever is greater). This is the first stage where the amount of tax owed starts to affect the penalty amount — meaning someone with a large tax bill faces a much larger penalty than someone who owes nothing.

If you owe nothing, the £300 minimum applies. If you owe £20,000, the penalty is £1,000 at this stage.

Stage 4 — Twelve months late: a further 5%

At twelve months late (from 1 February of the following year), another penalty of 5% of the tax owed is charged (again minimum £300). In cases where HMRC determines the failure was deliberate and concealed, the penalty can be as high as 100% of the tax owed.

Total maximum automatic penalty for filing a year late with no tax owed: £1,600 (£100 + £900 + £300 + £300).

For someone owing £50,000: the twelve-month penalty could reach £100 + £900 + £2,500 + £2,500 = £6,000 before interest on the unpaid tax.

Late payment penalties: separate from filing penalties

Even if you file your return on time, paying late triggers separate surcharges. These are calculated on the unpaid tax, not on the total liability.

• 30 days late: 5% surcharge on unpaid tax
• 6 months late: additional 5% surcharge
• 12 months late: additional 5% surcharge

So if you owe £10,000 and pay 12 months late, you'll accumulate surcharges of £500 + £500 + £500 = £1,500 in surcharges, plus interest on the unpaid tax throughout the period.

Interest on late tax

Completely separate from penalties, HMRC charges interest on unpaid tax from the due date until the date of payment. The interest rate is set at the Bank of England base rate plus 2.5%, reviewed periodically. At current base rates, this is around 7–8% per year — more than most savings accounts pay, so carrying a tax debt is rarely a sensible financial choice.

Interest is charged automatically and compounds. It cannot be appealed unless the underlying tax was wrongly assessed.

Payments on account and surcharges

Late payment surcharges also apply to late payments on account (31 January and 31 July deadlines). If you miss the 31 July payment on account, the 5% surcharge applies to the unpaid amount once it is 30 days late. The interest clock starts from 31 July.

Penalty notices and how HMRC communicates

HMRC sends penalty notices by post (and through the online Government Gateway account if you've opted in to online correspondence). These notices set out:

• The penalty amount
• The tax year and return it relates to
• The deadline for paying the penalty
• Your right to appeal

Penalties accrue interest if not paid promptly. Pay penalties at the same place you pay your Self Assessment tax — online through your Government Gateway account.

How to appeal a penalty

You can appeal a penalty if you have a reasonable excuse. HMRC defines reasonable excuse as something that was unforeseeable, outside your control, and that you acted on promptly once the obstacle was removed. Examples that are typically accepted:

• Serious illness or hospitalisation of the taxpayer (or immediate family member where they were responsible for your care)
• Death of a partner or close family member immediately before the deadline
• A Government Gateway technical failure on the deadline date itself (requires HMRC records to confirm)
• Postal failure for paper returns (where evidence of posting exists)

Examples that are not accepted:

• Not receiving a reminder from HMRC (you are responsible for knowing the deadlines)
• An accountant or tax adviser failing to file on time (the responsibility remains with the taxpayer)
• Forgetting the deadline
• Having insufficient funds to pay the tax (this may delay payment but does not excuse late filing)

To appeal, write to HMRC or use the online appeals process within 30 days of receiving the penalty notice. If your appeal is rejected, you can request a review by an independent HMRC officer, and ultimately appeal to the First-tier Tax Tribunal.

Special reduction: prompted and unprompted disclosures

If you have failed to file or declare income and wish to come forward, the penalty regime differs depending on whether you disclose before or after HMRC contacts you:

• Unprompted disclosure (you come forward before HMRC contacts you): penalties are significantly reduced, sometimes to zero for genuine mistakes
• Prompted disclosure (HMRC has already opened an enquiry): reduced penalties still apply, but the discount is smaller

If you have undisclosed income from previous years, HMRC's Worldwide Disclosure Facility or the regular disclosure process offers a structured way to come forward at reduced penalty rates.

The bottom line

The financial cost of missing the 31 January deadline for even a brief period is significant — £100 immediately, then £10 per day, then percentage surcharges. The administrative burden of appealing and the stress of managing a penalty notice makes the cost higher still. If you're struggling to gather your records or complete your return, the most cost-effective action is always to file on time with estimated figures and amend later — a late amendment triggers no penalty, whereas a late return does.

Keep a reminder in your calendar and use the Self Assessment Estimator throughout the year so the filing process never requires a last-minute scramble.