UK Self-Assessment Late Filing Penalties 2026
Missing the 31 January Self Assessment deadline triggers an instant £100 penalty even if you owe no tax — then £10/day from day 90, plus 5% surcharges at 6 and 12 months. Late payment adds 7.75% interest in 2026. Full penalty schedule.
The deadlines that matter
Two deadlines for the 2024/25 tax year (year of assessment ending 5 April 2025):
| Deadline | Date | What's due |
|---|---|---|
| Paper return | 31 October 2025 | Filing on paper SA100 |
| Online return | 31 January 2026 | Online filing AND balancing payment AND first payment on account |
| Second payment on account | 31 July 2026 | Second POA (for trading income) |
99% of taxpayers file online, so 31 January is the headline deadline.
Income Tax Calculator
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Open Income Tax calculatorThe late-filing penalty timeline (2026)
| Days late | Penalty | Cumulative |
|---|---|---|
| 1 day (1 Feb 2026) | £100 fixed | £100 |
| 3 months (1 May 2026) | £10/day, capped at 90 days = £900 | up to £1,000 |
| 6 months (1 Aug 2026) | Greater of 5% of tax due or £300 | £1,300+ |
| 12 months (1 Feb 2027) | Greater of 5% of tax due or £300 | £1,600+ |
The 6- and 12-month penalties can be uplifted to 70% or 100% of tax owed if HMRC believes the failure was deliberate or concealed.
The late-payment penalty timeline
Separate from filing penalties. Triggered if tax owed (the balancing payment plus first POA) isn't paid by 31 January 2026:
| Days late | Late payment penalty |
|---|---|
| 30 days (3 March 2026) | 5% of unpaid tax |
| 6 months | Another 5% of unpaid tax |
| 12 months | Another 5% of unpaid tax |
Plus daily interest at base rate + 2.5% = 7.75% annualised in May 2026.
Worked example — Jamie, £4,000 tax owed, files 10 months late
Jamie missed both deadlines and files on 30 November 2026. Tax owed: £4,000.
| Item | Amount |
|---|---|
| Fixed late-filing penalty | £100 |
| Daily penalties (90 days × £10) | £900 |
| 6-month filing penalty (5% × £4,000) | £200 → uplifted to £300 minimum |
| 6-month late-payment penalty (5% × £4,000) | £200 |
| 30-day late-payment penalty (5% × £4,000) | £200 |
| Interest (£4,000 × 7.75% × 10/12) | £258 |
| Total cost on top of £4,000 tax | £1,958 |
Jamie pays £5,958 instead of £4,000 — a 49% penalty multiplier for filing 10 months late.
Self-Employed Tax Calculator
Calculate income tax, Class 2 and Class 4 National Insurance for self-employed and sole traders for 2025/26.
Self-employed tax calculatorWorked example — Priya, £0 tax owed, files 4 months late
Priya is a PAYE employee who registered for Self Assessment because of a small side hustle. She filed on 31 May 2026 having earned £200 from freelance work — well within the £1,000 trading allowance, so tax owed is £0.
| Item | Amount |
|---|---|
| Fixed late-filing penalty | £100 |
| Daily penalties (1 May to 31 May = 31 days × £10) | £310 |
| Total penalty | £410 |
She owed nothing in tax — and the penalty is still £410. This is the most common gotcha: people assume "no tax, no penalty." Wrong.
What counts as a reasonable excuse
HMRC's guidance (CH71500) accepts these as reasonable:
- Bereavement of a partner or close family member shortly before the deadline.
- Serious illness of the taxpayer or a dependent, certified by a GP.
- HMRC IT or postal failures that prevented filing.
- UTR not issued in time despite registering before 5 October.
- Fire, flood or theft of records close to the deadline.
Not accepted:
- "I forgot."
- "My accountant let me down" (you remain responsible).
- "The system was complicated."
- "I was abroad / on holiday."
- "I couldn't afford the tax" (this is a payment issue, not a filing one — file first, then arrange Time to Pay).
You must file the return as soon as the excuse ends.
Appeal mechanics
- 30-day window from the date on the penalty notice (extended to 3 months if HMRC accepts).
- File the return first if not yet filed — most appeals fail on outstanding returns.
- Use SA370 or appeal via your personal tax account.
- HMRC review: typically 4–8 weeks for a decision.
- First-tier Tribunal if HMRC refuses — free, written process for most penalty cases.
Around 40% of appeals succeed at HMRC review stage, rising to 60% at tribunal for genuine reasonable-excuse cases.
Time to Pay — the way to stop late-payment penalties
If you've filed but can't pay by 31 January 2026:
- Set up a Time to Pay (TTP) arrangement online if you owe £30,000 or less and can clear within 12 months.
- Set up by 1 March 2026 to avoid the 30-day late-payment penalty.
- Interest still accrues at 7.75% on the unpaid balance, but no further fixed late-payment penalties.
See HMRC Time to Pay tax debt for the application steps.
What happens at 12+ months
After 12 months HMRC moves to:
- Determination assessment — HMRC estimates your tax and demands payment.
- Discovery assessment — opens enquiry windows up to 20 years for deliberate evasion.
- Magistrates' court for sums under £2,000 of penalty + tax.
- County court / High Court for larger amounts.
- Account freezing orders — HMRC can freeze bank accounts under POCA 2002 for serious deliberate non-compliance.
The escalation is real. Don't let a missed January deadline drift to a missed January-the-next-year deadline.
How to prevent missing again
- Register before 5 October of the year after the tax year (so 5 October 2025 for the 2024/25 return).
- Set a 31 December personal deadline. Treat January as buffer time.
- Save 25–30% of self-employed income in a separate account from day one.
- Use HMRC's Self Assessment app for reminders.
- Engage an accountant — agent filers had a 99.2% on-time rate in 2024/25 vs 95.1% self-filers.
- Run a dry calculation in November to know what's coming.
See our 31 January deadline checklist.
Try the calculator
Income Tax Calculator
Work out how much income tax you owe using the latest 2025/26 UK tax bands.
Income tax calculatorSelf-Employed Tax Calculator
Calculate income tax, Class 2 and Class 4 National Insurance for self-employed and sole traders for 2025/26.
Self-employed tax calculatorNational Insurance Calculator
Calculate your National Insurance contributions for 2025/26.
National Insurance calculatorSources
- HMRC: Self Assessment tax returns — Penalties
- Schedule 55 Finance Act 2009 (filing penalties); Schedule 56 (payment penalties)
- HMRC: Compliance Handbook CH71500 — Reasonable excuse
- HMRC: Interest rates for late and early payments
- HMRC: SA370 appeal form
Frequently asked questions
What is the penalty for filing Self Assessment late in 2026?
An automatic £100 fixed penalty as soon as you miss the 31 January 2026 deadline, even if you owe no tax or are due a refund. After 3 months HMRC adds £10 per day for up to 90 days (£900). At 6 months, 5% of tax due or £300, whichever is higher. At 12 months, another 5% or £300.
Can I avoid the £100 penalty if I owe no tax?
No. The £100 is a fixed filing penalty under Schedule 55 Finance Act 2009 — it applies to the act of not filing, regardless of tax owed. The only way to escape is a successful 'reasonable excuse' appeal.
What counts as a reasonable excuse?
Serious illness, death of a close relative, postal/IT failures preventing filing, and HMRC's own delays issuing a UTR. Forgetting, being too busy, or finding the system difficult are not accepted. You must file within a 'reasonable period' of the excuse ending.
What is the late payment interest rate in 2026?
HMRC late-payment interest tracks the Bank of England base rate plus 2.5%. With base rate at 5.25% in May 2026, late-payment interest is 7.75% (annualised, accrued daily) on any unpaid tax from 1 February 2026.
Can I appeal a late filing penalty?
Yes, within 30 days of receiving the penalty notice. Use form SA370 or appeal in your personal tax account. You must show a 'reasonable excuse' that prevented timely filing.
Try the calculators
Income Tax Calculator
Work out how much income tax you owe using the latest 2025/26 UK tax bands.
Self-Employed Tax Calculator
Calculate income tax, Class 2 and Class 4 National Insurance for self-employed and sole traders for 2025/26.
Take-Home Pay Calculator
Calculate your net salary after income tax, National Insurance and student loan deductions.
National Insurance Calculator
Calculate your National Insurance contributions for 2025/26.
In-depth guides
Related reading
UK Self Assessment From Scratch — Part 3: Declaring Every Type of Income
Part 3 of our Self Assessment series — how to declare employment, self-employed, dividend, rental, foreign, savings, crypto and CGT income on your UK tax return. With the boxes to fill, evidence to keep, and common errors.
UK Self Assessment From Scratch — Part 2: UTR and Government Gateway Setup
Step-by-step guide to registering for Self Assessment, getting your UTR (Unique Taxpayer Reference) number, setting up your HMRC Government Gateway account and what to do if things go wrong.
Self-Employed Class 4 NI 2025/26: The 6% Rate Explained
Self-employed Class 4 National Insurance fell to 6% on profits between £12,570 and £50,270 from April 2024 and stays there for 2025/26. Here's how it works, who pays, and worked examples on real profit figures.