Quick answer
HMRC does not grant extensions to the 31 January Self Assessment deadline. You can avoid penalties only by filing on time or showing a reasonable excuse for lateness.
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Why there is no extension
The deadline is set by law, so HMRC cannot move it for individuals. Even if you are waiting on paperwork from a third party, the deadline stays the same.
What you can do instead
File using your best estimates and mark them as provisional, then amend the return later within 12 months of the deadline. This avoids the £100 late filing penalty.
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Reasonable excuse
Serious illness, bereavement or a failure of HMRC systems can justify late filing without penalty if you file soon after the problem ends.
Plan ahead for next year
Set up your online account early, start gathering records in April and file well before the January rush. An accountant can handle this for a fixed fee.
How the penalty clock runs
Because the 31 January deadline is fixed, the sensible way to think about an extension is to understand exactly what happens if you miss it. The late filing penalty system is built in stages. A fixed £100 penalty applies immediately if the return is not filed by the deadline, even if no tax is due. If the return is still outstanding after three months, daily penalties of £10 a day build up for up to 90 days, a maximum of £900. At six months a further penalty applies of 5% of the tax due or £300, whichever is higher, and the same again at twelve months. Late payment is a separate regime: 5% of the unpaid tax at 30 days, a further 5% at six months and another at twelve months, plus interest at Bank Rate + 4%.
Worked example: a return filed seven months late
This is an illustrative example. A sole trader owes £4,000 for the tax year, does not file or pay on 31 January, and files and pays seven months later.
| Penalty | Working | Amount |
|---|---|---|
| Initial late filing | Fixed | £100 |
| Daily penalties | 90 days x £10 | £900 |
| Six-month filing penalty | 5% x £4,000 = £200, so the £300 minimum applies | £300 |
| Late payment at 30 days | 5% x £4,000 | £200 |
| Late payment at six months | 5% x £4,000 | £200 |
| Total penalties | £100 + £900 + £300 + £200 + £200 | £1,700 |
Interest at Bank Rate + 4% is added on top. The penalties here equal 42.5% of the £4,000 tax bill (£1,700 / £4,000). The cost of an hour of an accountant’s time is trivial by comparison, which is why the focus should be on filing on time rather than looking for an extension. Our guide to late payment penalties explains the payment side in more detail.
Options if you genuinely cannot meet the deadline
There is no general extension, but a few routes can help. If you cannot pay in full, contact HMRC about Time to Pay, which is generally available for debts under £30,000. If you were prevented from filing by something outside your control, such as serious illness, you may have a reasonable excuse, which must be put to HMRC and which applies only for as long as the circumstances lasted. See our reasonable excuse examples. A paper return has an earlier deadline of 31 October, so it gives less time, not more, and online filing is the better choice for anyone short of time. If you are using provisional figures, you can file an estimate and amend within 12 months of the 31 January deadline.
Common mistakes
- Believing that telling HMRC you will be late stops a penalty.
- Waiting for missing paperwork rather than filing on a best-estimate basis and correcting later.
- Leaving the Government Gateway and UTR sorting until January.
- Mixing up the 31 October paper deadline with the 31 January online deadline.
- Forgetting the 31 July second payment on account.
Practical checklist
- Confirm you can log in to your HMRC online account well before the deadline.
- Collect income and expense records by the end of the tax year, 5 April.
- Set an internal deadline several weeks before 31 January.
- Ask for help early if records are incomplete.
- Follow our 31 January 2027 preparation plan.
Directors should also read director tax return deadlines and penalties.
How SATR can help
We prepare and file returns online for a fixed fee from £199 + VAT. If you have already missed a deadline, our late Self Assessment tax return service can help you get back on track.
This article is general information, not personal tax advice.
Filing with estimates and correcting later
A common reason people ask about extensions is that a figure is missing: a pension statement has not arrived, a landlord’s agent has not sent annual statements, or a dividend voucher cannot be found. In many cases the better answer is to file on time using a reasonable and honest estimate, flag it as provisional where the form allows, and amend the return once the final figure is available. You can generally amend within 12 months of the 31 January deadline. This protects you from the filing penalties while keeping the return accurate. Do not guess wildly, though: estimates should be your best assessment based on the information you have, and any later difference should be corrected promptly.
If you also have payments to make, remember that the payment deadline is the same as the filing deadline. Filing on time but paying late still attracts late payment penalties and interest, so keep cash set aside as you go.
Frequently asked questions
Can I file after 31 January without penalty?
Only if HMRC accepts you had a reasonable excuse. Otherwise a £100 penalty applies immediately.
Can estimates be used?
Yes, if you cannot get exact figures, use reasonable estimates, tell HMRC they are provisional and update them later.
Tax rules and rates change. Figures here reflect 2025/26 guidance; always check current HMRC rules or ask us before acting.
Can I get more time if my accountant is delayed?
No. An accountant being busy is not usually a reasonable excuse, and the deadline stays the same. Instruct help early and give records promptly.
Do I pay penalties if I am owed a refund?
The £100 late filing penalty can apply even where no tax is due, so file on time regardless. Check current HMRC guidance on how penalties are treated in your situation.
What is the latest I can file without a penalty?
The online deadline is 31 January after the end of the tax year. A paper return must be filed by 31 October.
Don’t leave your tax return to the last minute. Avoid penalties, save time, and let an expert take care of it for you.
Related guides
- Self Assessment Deadline 31 January 2027: Preparation Plan
- What to Do If HMRC Opens an Enquiry Into Your Tax Return
- How to Claim a Self Assessment Tax Refund
- late Self Assessment service
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