The short answer: the deadline for online Self Assessment returns for the 2025 to 2026 tax year is 31 January 2027, and any tax you owe is due the same day. If you have not started, there is still time if you act now. File on time even if you cannot pay everything: filing late and paying late are penalised separately, so filing on time avoids the late filing penalty while you sort out payment.
Step 1: check you are registered
If this is your first Self Assessment return, you needed to tell HMRC by 5 October 2026. If you missed that, register now. When you register after 5 October, HMRC sends you a letter or email with a different deadline for your return: 3 months from the date on that letter or email.
Registering late can still lead to a penalty if your tax is not paid in full by 31 January, so do not wait.
Step 2: make sure you can sign in
Check now that you can sign in to your HMRC online account. Setting up access or recovering lost sign-in details can take time, and the last week of January is the worst time to find out there is a problem.
Step 3: gather your records
You will need your income, your business expenses, any rental income and costs, interest and dividends, and pension contributions. Our checklist of what to bring to your accountant covers the full list, and our guide to allowable expenses helps you make sure you are not paying more tax than you need to.
Step 4: file by 31 January 2027
File online by 11:59pm on 31 January 2027. If you would like tax you owe collected through your tax code instead, and you are eligible for that, the return needs to be filed online by 30 December 2026.
Step 5: pay what you can, and talk to HMRC about the rest
Tax owed for 2025 to 2026 is due by 31 January 2027, together with your first payment on account for 2026 to 2027 if you make them (see our guide to payments on account). If you cannot pay in full, you may be able to set up a payment plan with HMRC to pay in instalments. Contact HMRC, or ask us, as early as you can.
What it costs to be late
| When | Filing late | Paying late |
|---|---|---|
| Straight away | £100 | Interest on the amount owed |
| After 30 days | – | 5% of the tax unpaid |
| After 3 months | £10 a day, up to £900 | – |
| After 6 months | 5% of the tax due or £300, whichever is greater | A further 5% of the tax unpaid |
| After 12 months | A further 5% or £300, whichever is greater | A further 5% of the tax unpaid |
Penalties must be paid within 30 days of the date on the penalty notice. Interest keeps adding up until the tax is paid.
If you have already missed a deadline
File and pay as soon as you can: the longer a return is late, the more the penalties grow. If something serious stopped you meeting the deadline, you may be able to appeal. You usually have 30 days from the date of the penalty to appeal.
HMRC’s examples of a reasonable excuse include the death of a partner or close relative shortly before the deadline, an unexpected stay in hospital, your computer or software failing while you were preparing your online return, and a fire, flood or theft. Not having enough money to pay, finding the online system too difficult, or not getting a reminder from HMRC do not count. Once the problem is over, you must send your return or payment as soon as you can.
Several years behind?
If you have not filed for more than one year, it is better dealt with than left. Talk to us. We will look at what is outstanding, put the years in order and deal with HMRC for you, so you know where you stand.
How we help
Send us what you have and we will tell you what is missing, prepare your Self Assessment tax return, tell you what to pay and when, and file it for you. Our fee is agreed in writing before we start. The sooner you get in touch, the easier it is to meet the deadline.
Sources: gov.uk, Self Assessment tax returns: deadlines and penalties; Register for Self Assessment; Disagree with a tax decision or penalty: reasonable excuses; If you cannot pay your tax bill on time. Checked 3 October 2026.
Common questions
Can I file my return before I have the money to pay?
Yes. Filing and paying are separate. Filing by 31 January 2027 avoids the late filing penalty even if you need more time to pay. Talk to HMRC, or to us, about paying the rest.
I registered after 5 October. When is my deadline?
HMRC will send you a letter or email with your deadline, which is 3 months from the date on it. A penalty can still apply if your tax is not paid in full by 31 January.
Can I appeal a late filing penalty?
Yes, if you had a reasonable excuse, such as an unexpected stay in hospital or a close bereavement shortly before the deadline. You usually have 30 days from the date of the penalty to appeal.
Is it too late to ask an accountant in January?
Not necessarily, but the earlier the better. Contact us with what you have and your deadline, and we will tell you honestly whether we can meet it.
General information only, not personal advice. Tax rules, rates and thresholds change, so check gov.uk or speak to us about your own situation.