Self Assessment Late Filing Penalty: Amounts and Appeals

Quick answer: The Self Assessment late filing penalty starts at £100 the day after the deadline, even if no tax is owed. After 3 months HMRC adds £10 a day up to £900, then 5% of the tax due or £300 (whichever is greater) at 6 months and again at 12 months. Late payment brings separate 5% penalties plus interest.

Missing the 31 January deadline is one of the most common and most expensive admin mistakes freelancers and sole traders make. The Self Assessment late filing penalty is automatic, it applies even when you owe nothing, and it escalates quickly if you leave the return unfiled. This guide explains every penalty as of 2026, how late payment penalties and interest stack on top, how to appeal with a reasonable excuse, and how to stop it happening again. For the filing process itself, see our step-by-step guide to the Self Assessment tax return.

Note: This is general information, not tax advice. Penalty rules depend on your circumstances, so check GOV.UK or speak to an accountant.

Self Assessment deadlines for 2025/26

The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. The key dates are:

• 5 October 2026: deadline to register for Self Assessment if you became newly self-employed during 2025/26. Our guide to registering as self-employed explains how.
• 31 October 2026: paper return deadline.
• 31 January 2027: online return deadline, and the deadline to pay the balancing payment and the first payment on account for 2026/27.
• 31 July 2027: second payment on account for 2026/27.

Penalties are triggered by whichever deadline applies to the way you file. If you missed the paper deadline, you can still file online by 31 January without a penalty.

Every Self Assessment late filing penalty, step by step

GOV.UK sets out the Self Assessment penalties as follows:

How late the return is	Penalty	Running total (minimum)
1 day	£100 fixed penalty	£100
3 months	£10 a day for up to 90 days, maximum £900	£1,000
6 months	5% of the tax due or £300, whichever is greater	£1,300
12 months	Another 5% of the tax due or £300, whichever is greater	£1,600

The running total column shows the minimum for someone who owes little or no tax. Where the tax due is large, the 5% charges exceed £300 and the total grows. For partnership returns, every partner is charged a penalty if the partnership return is late.

Why the £100 penalty applies even if you owe nothing

The filing penalty is for not sending the return, not for the tax. If HMRC issued you a notice to file, the return is due whether or not you made a profit. If you have stopped trading or your income now falls under the £1,000 trading allowance, ask HMRC to withdraw the notice before the deadline instead of simply not filing.

Late payment penalties and interest

Paying late is a separate failure with separate charges. If your tax is not paid by the due date, HMRC charges:

• 5% of the tax unpaid at 30 days.
• Another 5% of the tax still unpaid at 6 months.
• Another 5% of the tax still unpaid at 12 months.
• Interest on the unpaid amount from the due date until it is paid.

HMRC's late payment interest rate is the Bank of England base rate plus 4 percentage points. According to HMRC's published rates, it has been 7.75% a year since 9 January 2026. Interest also runs on late payments on account, which surprises many people in their second year of self-employment.

There is also a failure to notify penalty for people who register late, after 5 October, and do not pay all their tax by 31 January. It is based on the tax still unpaid.

How HMRC tells you about a penalty

Penalties arrive as penalty notices by post or in your online account, and later charges such as the daily penalties and the 6-month penalty arrive as separate notices. GOV.UK says to pay a penalty within 30 days of the date on the notice. Each notice also starts its own 30-day window for an appeal, so note the date as soon as it arrives. If you are appealing, you do not have to wait for HMRC to finish adding penalties before you write; you can ask for the appeal to cover all the penalties charged for that return.

Worked example: a return filed six and a half months late

Priya is a freelance copywriter. Her 2025/26 return was due online on 31 January 2027. She files it on 15 August 2027, and her tax bill is £4,000, which she pays the same day.

Penalty	Calculation	Amount
Initial late filing	Fixed	£100
Daily penalties	90 days x £10 (cap reached)	£900
6-month penalty	Greater of 5% x £4,000 = £200 or £300	£300
Late payment at 30 days	5% x £4,000	£200
Late payment at 6 months	5% x £4,000	£200
Total penalties	£100 + £900 + £300 + £200 + £200	£1,700

On top of that, interest runs on £4,000 for about six and a half months. At 7.75% a year, a rough estimate is £4,000 x 7.75% x 6.5 / 12, about £168. Priya's late return costs her roughly £1,868 more than filing and paying on time: nearly half of her original tax bill. Had she filed on time and only paid late, she would have avoided £1,300 of that.

How to appeal a Self Assessment late filing penalty

If something genuinely stopped you filing on time, you can appeal. HMRC's guidance on reasonable excuses describes it as something that stopped you meeting a tax obligation for a valid reason.

What HMRC accepts as a reasonable excuse

• Your partner or another close relative died shortly before the deadline.
• An unexpected stay in hospital or a serious or life-threatening illness.
• Your computer or software failed while you were preparing your online return.
• Service issues with HMRC online services.
• A fire, flood or theft that prevented you filing.
• Postal delays you could not have predicted.
• Delays related to a disability or mental health condition.
• You relied on someone else, such as an agent, to send the return and they failed to.

In every case you must file as soon as possible after the excuse ends.

What does not count

• You did not have the money to pay.
• You found the online system too difficult.
• You did not receive a reminder from HMRC.
• You made a mistake on your return.

Steps to appeal

1. File the overdue return first. An appeal is far weaker if the return is still outstanding.
2. Check the date on the penalty notice. You usually have 30 days from that date to appeal, according to GOV.UK's page on disagreeing with a tax penalty.
3. Use the appeal form sent with the penalty, or write a signed letter to HMRC.
4. Include the essentials: your name, Unique Taxpayer Reference, why the return was late, and the dates the problem started and ended.
5. Attach evidence: hospital letters, error messages and screenshots with dates, or correspondence with your agent.
6. If HMRC rejects the appeal, you will be offered a review, and you can take the case to the tax tribunal.

Writing a strong appeal

Successful appeals are specific and dated. A weak appeal says "I was ill around the deadline." A strong one says "I was admitted to hospital on 24 January 2027 and discharged on 12 February 2027, as shown by the enclosed discharge letter. I filed my return online on 16 February 2027, four days after leaving hospital." It explains what happened, shows it was outside your control, gives evidence, and shows you acted promptly once the problem ended. Keep a copy of everything you send and a note of the date you posted it.

What to do if you have already missed the deadline

If 31 January has passed and your return is not in, the most expensive thing you can do is wait. The £100 penalty is already fixed, but the daily penalties only start three months after the deadline, and the 5% charges at six and twelve months can still be avoided. Work through these steps in order:

1. Sign in to your HMRC online account and check which returns are outstanding and what HMRC thinks you owe. If you cannot find your Unique Taxpayer Reference, it appears on previous returns, penalty notices and HMRC letters.
2. Gather your income records. Total every invoice issued in the tax year, add any other income, and pull together your expense receipts. If records are incomplete, use bank statements to rebuild them.
3. File the return online as soon as it is ready. Even a few days can matter if you are close to the three-month point, when £10 a day begins.
4. Pay what you can immediately. Every payment reduces the base for the 5% late payment penalties and for interest.
5. Arrange a payment plan for the rest. If you cannot clear the bill, apply for Time to Pay rather than letting the debt sit.
6. Decide whether you have grounds to appeal. If a reasonable excuse applies, appeal within 30 days of the penalty notice.

Penalties are separate for each return

If you have missed more than one year, each return carries its own set of penalties. Two years of unfiled returns for someone with little tax to pay can therefore cost twice the £1,600 minimum once both are more than 12 months late. Tackle the oldest return first, because it is the one closest to the next penalty point.

Late payments on account

Payments on account work differently from the balancing payment. If a payment on account is late, HMRC charges interest on it from the due date, while the 5% late payment penalties are aimed at the tax still unpaid after the final deadline for the year. That still makes paying on time worthwhile: interest at 7.75% adds up, and a missed July payment is often a sign that January will be difficult too.

The new penalty system for Making Tax Digital

HMRC has introduced a points-based late submission regime and a revised late payment penalty for people in Making Tax Digital for Income Tax. For volunteers, each late tax return earns a point, and reaching 2 points triggers a £200 penalty. Late payment penalties under the new system start at 3% of tax unpaid at day 15, another 3% at day 30, then 10% a year on the outstanding amount. HMRC writes to tell you when the new rules apply to you. Most people filing a normal 2025/26 return are still on the traditional penalties described above.

Late filing vs late payment: which costs more?

Scenario (tax due £4,000)	Filed on time, paid 6 months late	Filed 6 months late, paid on time
Filing penalties	£0	£1,300
Late payment penalties	£400	£0
Interest (approx.)	£155	£0
Total	About £555	£1,300

The interest figure is a rough estimate: £4,000 x 7.75% x 6 / 12 = £155. The lesson is simple: always file on time, even if you cannot pay. Then ask HMRC for a Time to Pay arrangement for the tax.

How to make sure you never miss the deadline again

• Keep invoices and expenses up to date monthly. Most late returns are late because the records are a mess. Our allowable expenses guide shows what to track.
• Number and file every invoice. Creating invoices in the UK invoice generator and saving each PDF gives you a ready income record.
• File early in the autumn. You can submit any time after 6 April. Filing early does not make you pay early, but it tells you the bill months in advance.
• Save for tax as you invoice. Setting aside a fixed share of every payment avoids a cash crunch in January. Remember Class 4 National Insurance is due on top of income tax.
• Use a year-end routine. Our year-end invoicing checklist helps you close the books cleanly.

Avoid the Self Assessment late filing penalty with better records

The Self Assessment late filing penalty is entirely avoidable: file by 31 January even if you cannot pay, appeal within 30 days if you had a genuine reasonable excuse, and keep records that make the return quick to complete. Start with clean, numbered invoices from the free invoice generator and pick a simple layout such as the minimal invoice template, so your income figures are ready when tax season arrives. Your finished invoice downloads as a PDF, free and with no sign-up.