The 31 January deadline has passed and your Self Assessment return is not filed. You are now in a race, not against HMRC exactly, but against a penalty clock that started the moment the deadline passed and compounds the longer the return stays outstanding.
The difference between acting today and acting in three months is large and measurable. Below are the three things to do, in the order that matters, plus what each penalty stage actually costs so you can see why the sequence is worth getting right.
Thing 1: file the return now, even if it is not perfect
The most expensive mistake after a missed deadline is waiting until everything is perfectly organised before filing. While you gather receipts, the penalty clock keeps running.
HMRC accepts a return filed on reasonable estimated figures, with a note that an amendment will follow once your records are complete. Filing on estimates stops the daily penalty from accruing once the three-month threshold is reached, removes the risk of HMRC issuing its own determination of what you owe, and lets a penalty appeal be processed. If you would rather not do it under time pressure, a specialist can file a late return, usually within 48 hours.
A filed return on honest estimates now beats a perfect return that is still three months away. File something accurate enough today and correct it later.
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Thing 2: check your appeal window before it closes
Once the return is filed, you have 30 days from the date on each penalty notice to appeal that penalty on reasonable excuse grounds. The window is fixed. Miss it and you can still appeal, but you first have to justify why the appeal itself is late, which is a higher bar.
Look at the date on the penalty letter and count 30 days forward. The grounds HMRC accepts include serious illness affecting you or a close relative, a bereavement, an unexpected hospital admission, a fire, flood or theft, and HMRC system failures. The grounds it rejects include pressure of work, not knowing the deadline existed, and finding the return too complicated. The full breakdown of which excuses HMRC accepts and rejects is here, and the SA370 appeal form is explained step by step here.
Even without an obvious excuse, do not assume an appeal is hopeless. A specialist who builds these appeals regularly knows the framing and evidence that give the best chance.
Thing 3: sort the underlying tax, or arrange a plan
Filing stops the filing penalties escalating, but the tax is a separate matter. HMRC charges interest on unpaid tax from 31 January, compounding daily, so dealing with the filing while ignoring the payment lets interest build throughout.
If you cannot pay in full, a Time to Pay arrangement spreads the bill over monthly instalments and stops enforcement action while it runs. Debts under £30,000 can usually be set up online. For larger amounts you negotiate directly, and a specialist who presents the financial case to HMRC can make a real difference to the terms. The detail of how HMRC collects unpaid tax, and how Time to Pay stops it, is covered here.
What each stage costs if you do nothing
The penalties are designed to escalate sharply, which is exactly why filing early is worth so much. The figures below assume a £5,000 tax bill.
Penalty escalation if the return stays unfiled (£5,000 tax owed)
| How late | What is added | Running penalty total |
|---|---|---|
| 1 day | £100 fixed penalty | £100 |
| 3 months | £10 per day, up to £900 | up to £1,000 |
| 6 months | 5% of tax, £300 minimum | £1,300 |
| 12 months | A further 5%, £300 minimum | £1,600 |
The full penalty escalator and how to stop it is set out here. The pattern holds on any bill: the daily charges are fixed, and the 5% surcharges scale with the tax owed.
Why the order matters
File first, appeal second, sort the payment third. The sequence matters because HMRC will not process a penalty appeal while the return is outstanding, and a Time to Pay plan is easier to agree once the return is filed and HMRC can see the actual liability. Trying to do all three at once, or waiting until time, records and money line up together, is how a manageable problem drifts past the three-month threshold and becomes a much larger one.
Common questions after a missed deadline
How much is the penalty if I file a few days late?
A return filed any time after the deadline triggers the £100 fixed penalty, even by a single day and even if no tax is due. The daily £10 charges do not start until the return is three months late, so filing within those first weeks keeps the exposure at £100.
Is the deadline different for paper returns?
Yes. The paper filing deadline is 31 October; the online deadline is 31 January. Almost everyone now files online, so 31 January is the date that applies to most people. The payment deadline for tax owed is also 31 January.
I have never filed before and only just registered. What now?
File as soon as your Government Gateway account is active, on estimates if needed, and keep a record of when you registered. Genuine confusion over a first-time filing obligation, with no prior pattern of notices, is sometimes accepted as a reasonable excuse, so it is worth appealing.
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