UK Self Assessment deadlines and how penalties escalate
Self Assessment has four deadlines, not one, and the penalty for missing the filing date is charged whether or not you owe any tax. A nil return filed twelve months late costs £1,600 in filing penalties alone.
The four dates
| Deadline | What is due |
|---|---|
| 5 October | Register for Self Assessment if newly liable (following the tax year end) |
| 31 October | Paper return |
| 31 January | Online return, balancing payment, and first payment on account |
| 31 July | Second payment on account |
For the 2026/27 tax year (6 April 2026 to 5 April 2027) that means a paper return by 31 October 2027 and an online return with payment by 31 January 2028. Filing online buys three extra months over paper, which is why roughly nine in ten filers use it.
One under-used date: file online by 30 December and, if you owe less than £3,000 and have PAYE income, HMRC can collect the tax through your tax code for the following year instead of demanding it in January.
The filing penalty ladder
Set out in Schedule 55 of the Finance Act 2009, and automatic.
| How late | Penalty | Cumulative on a nil-tax return |
|---|---|---|
| 1 day | £100 fixed | £100 |
| 3 months | £10 per day, up to 90 days | £1,000 |
| 6 months | Greater of £300 or 5% of tax due | £1,300 |
| 12 months | Greater of £300 or 5% of tax due | £1,600 |
Because the 6- and 12-month charges have a £300 floor, the ladder does not shrink to nothing on a small liability. Where HMRC finds the failure deliberate and concealed, the 12-month charge can rise to 100% of the tax.
We prepare accounts, Corporation Tax and Self Assessment work with a UK-qualified professional on the engagement.
Avail our UK tax desk servicesLate payment is a separate ladder
Under Schedule 56 of the Finance Act 2009, and it stacks on top of the filing penalties rather than replacing them.
| How late | Penalty on unpaid tax |
|---|---|
| 30 days | 5% |
| 6 months | A further 5% |
| 12 months | A further 5% |
Fifteen per cent in total if the balance sits unpaid for a year, plus daily interest running from 1 February.
A worked penalty position
Take someone owing £8,000 for 2026/27 who files and pays six months late.
| Charge | Basis | Amount |
|---|---|---|
| Fixed filing penalty | Day 1 | £100 |
| Daily filing penalties | 90 days × £10 | £900 |
| 6-month filing penalty | Greater of £300 or 5% of £8,000 | £400 |
| 30-day late payment penalty | 5% of £8,000 | £400 |
| 6-month late payment penalty | 5% of £8,000 | £400 |
| Penalties before interest | £2,200 |
That is 27.5% of the tax, on top of the tax, before interest. And note which charges dominate: £1,400 of the £2,200 is filing penalties, which would have been avoided entirely by submitting the return on time and paying late. The single most valuable action if you cannot pay is to file anyway.
If you cannot pay
File on time to stop the filing ladder, then deal with the money separately. HMRC's Time to Pay arrangements can spread the balance; agreeing one before penalties bite generally prevents the late-payment charges from accruing while the plan is honoured. Interest still runs.
Appealing a penalty
Appeal on form SA370 within 30 days of the penalty notice, on the basis of a reasonable excuse — serious illness, a bereavement, or an unavoidable failure of HMRC's own service. Pressure of work, lack of funds and reliance on someone else are generally not reasonable excuses. If you have been asked to file but believe you should not have been, ask HMRC to withdraw the notice rather than ignoring it; once withdrawn the penalty falls away, but ignoring a notice removes the argument.
Where this goes wrong
- Assuming no tax means no penalty. The £100 is triggered by lateness, not by liability.
- Treating filing and payment as one deadline. They are separate ladders and they stack.
- Missing 5 October registration. Without a UTR you cannot file, and a failure-to-notify penalty is geared to the tax.
- Forgetting 31 July. The second payment on account is easy to overlook — see payments on account.
- Appealing late. The window is 30 days from the notice.
Related: registering for Self Assessment and self-employed National Insurance.
Sources
This guide is written against the official and clearly labelled professional references below. Rates, thresholds and portal procedures change between reviews, so open the primary source before relying on a figure.
Questions people also ask
What are the two filing deadlines?
For a tax year ending 5 April, a paper return is due by 31 October and an online return by 31 January following. Most people file online, so 31 January is the date that matters — and it is also when the money is due.
Do I pay on the same day I file?
Yes for the balancing payment, which falls on 31 January alongside the online filing deadline. The first payment on account for the next year is also due that day, which is why January bills are often larger than expected.
What is the penalty for filing one day late?
A fixed penalty applies immediately once the deadline passes, regardless of whether tax is owed. Further penalties accrue as the delay lengthens, and they are separate from interest on unpaid tax.
Can I appeal a late filing penalty?
HMRC will consider a reasonable excuse, which has a narrower meaning than the everyday sense. Being busy or finding the return difficult does not qualify; serious illness or a genuine service failure might.
What if I owe nothing?
File anyway if you have been issued a notice to file. The fixed penalty applies to the failure to file, not to the failure to pay, so a nil return submitted late still attracts it.
Send the tax year and the transaction or filing involved, and we will tell you what is actually required.
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