If you are self-employed, a landlord, or a company director with untaxed income, one date should already be in your diary: 31 January 2027. That is the deadline to file your Self Assessment tax return online and pay the tax you owe for the 2025/26 tax year. Miss it by a single day and HMRC charges you £100, even if you owe no tax at all. Miss it by months, and filing penalties, payment penalties and interest start stacking on top of each other.
First, the naming confusion: which tax year is due when?
Self Assessment deadlines are easy to mix up because the tax year and the filing year are different. The tax year runs from 6 April to the following 5 April, and the return for that year is due the January after it ends.
So the return due on 31 January 2027 covers the 2025/26 tax year, from 6 April 2025 to 5 April 2026. The return for the current 2026/27 tax year is not due until 31 January 2028.
Who has to file Self Assessment?
You generally need to file if your tax is not fully collected through PAYE: sole traders and partners, landlords with rental income, company directors with dividends or other untaxed income, and higher earners with income over £100,000. If you are unsure, HMRC has a short online checker on GOV.UK.
If you need to file for the first time, you must register with HMRC by 5 October following the tax year. For the 2025/26 return, that was 5 October 2026. If you missed it, register as soon as possible: a failure-to-notify penalty normally only bites if tax is also left unpaid after 31 January. For the 2026/27 tax year, the registration deadline is 5 October 2027.
The key dates, in order
Here are the dates that matter for the 2025/26 return and the year that follows:
- 5 October 2026: registration deadline for first-time filers for 2025/26.
- 31 October 2026: paper return deadline for 2025/26, now passed, so online filing is the only practical route left.
- 30 December 2026: file online by this date if you want tax owed under £3,000 collected through your PAYE tax code, where eligible.
- 31 January 2027, by 11:59pm: online return deadline, balancing payment, and first payment on account for 2026/27, all on the same day.
- 31 July 2027: second payment on account for 2026/27.
- 5 October 2027: registration deadline for first-time filers for 2026/27.
- 31 January 2028: online return and payment deadline for the 2026/27 tax year.
One warning about 31 January 2027: it falls on a Sunday. You can file online that day, but a bank payment may not reach HMRC until the next working day, so aim to have the money with HMRC by Friday 29 January 2027.
Payments on account: the bill that surprises first-time filers
Payments on account are advance payments towards next year’s tax bill. HMRC normally asks for them when your Self Assessment bill was £1,000 or more and less than 80% of your tax was collected at source, for example through PAYE. Each payment is normally half of your previous year’s Income Tax and Class 4 National Insurance bill.
Here is a worked example. Suppose your 2024/25 bill was £6,000, so your payments on account for 2025/26 are £3,000 each, due on 31 January 2026 and 31 July 2026. Now suppose your actual 2025/26 bill turns out to be £9,000. On 31 January 2027 you owe the balancing payment of £3,000 (the £9,000 bill minus the £6,000 already paid) plus the first payment on account for 2026/27, half of £9,000, or £4,500. Your total January 2027 payment is therefore £7,500, not £3,000.
If you expect your income to fall, you can ask HMRC to reduce your payments on account, but only with a genuine basis for expecting a lower bill. If the reduction turns out to be too large, HMRC charges interest on the shortfall.
Late filing penalties: how £100 becomes £1,300
Late filing penalties apply even if you owe no tax and even if you are due a refund. They build up in stages:
- One day late: an automatic £100 fixed penalty.
- Three months late: £10 a day for up to 90 days, up to £900 on top of the £100.
- Six months late: a further penalty of 5% of the tax due or £300, whichever is greater.
- Twelve months late: another 5% of the tax due or £300, whichever is greater.
For example, suppose your tax bill is £4,000 and your return is six months late. Your filing penalties are £100, plus £900 of daily penalties, plus £300, since 5% of £4,000 is £200 and the £300 minimum applies. That is £1,300 in filing penalties alone, before payment penalties or interest.
Late payment penalties and interest: a second, separate bill
Filing late and paying late are penalised separately, and the two sets of charges run at the same time. For late payment, HMRC charges interest on the unpaid amount from the due date, at the Bank of England base rate plus 4%, plus penalties of 5% of the unpaid tax at 30 days late, another 5% at six months, and another 5% at twelve months.
Returning to the £4,000 example, six months late on payment adds 5% at 30 days (£200) and another 5% at six months (£200), plus interest. Combined with the £1,300 of filing penalties, the extra cost at six months is £1,700 plus interest. So the single most useful step, if you are already late, is to file the return now even if you cannot pay in full yet: filing stops the filing-penalty clock, even though payment penalties and interest continue until the tax is paid.
What if you have a reasonable excuse?
You can appeal a penalty if you had a reasonable excuse, meaning something genuinely outside your control that stopped you filing or paying on time. Examples that tend to succeed include a serious illness or bereavement close to the deadline, a documented HMRC system failure, or a genuine postal delay you can evidence. Forgetting the deadline, not having enough money to pay, and blaming an accountant without showing that you chased them routinely fail.
You must also put things right without unreasonable delay once the excuse ends, and keep evidence from the time, such as medical letters or dated emails. If your first appeal is refused, you can ask for an internal review before considering the First-tier Tribunal.
If you cannot pay: Time to Pay
If you cannot pay the full bill by 31 January, contact HMRC early rather than waiting for a penalty letter. HMRC may agree a Time to Pay arrangement, letting you spread the bill in monthly instalments. Online arrangements are generally available for smaller debts where you have filed all your returns and have no other overdue tax debts. Such an arrangement does not erase penalties already incurred, and interest still runs on the balance.
Making Tax Digital: does it change these deadlines?
Making Tax Digital for Income Tax started on 6 April 2026 for sole traders and landlords with qualifying income over £50,000, meaning gross self-employment and property income before expenses, not profit. Those in scope keep digital records and send quarterly updates through compatible software, then submit a final declaration by 31 January after the tax year. The threshold falls to £30,000 from April 2027 and £20,000 from April 2028.
For the return due on 31 January 2027, the traditional penalties above still apply, because that return covers 2025/26, before MTD mandation began. MTD filers move to a points-based system for missed submissions, with a £200 penalty once the points threshold is reached, and HMRC has confirmed no penalty points for late quarterly updates in the first year, 2026/27. The payment date does not change under MTD.
A practical checklist before 31 January 2027
- Confirm whether you need to file, using the GOV.UK checker if unsure, and register immediately if you have not.
- Gather your records now: invoices, bank statements, expense receipts, and rental or employment income details.
- File early, even if you cannot pay yet: filing stops filing penalties and gives you time to arrange payment.
- Work out your full January payment, including the balancing payment and the first payment on account.
- If the bill is unaffordable, contact HMRC about Time to Pay before the deadline.
- Set a reminder for 31 July 2027 for the second payment on account.
Frequently asked questions
Do I get a penalty if I file late but owe nothing?
Yes. The £100 fixed penalty applies as soon as the return is late, even if no tax is due or a refund is owed.
I filed on time but paid late. Am I in the clear?
No. Late payment penalties and interest apply separately from filing penalties, so the 5% payment penalties and interest still run on unpaid tax.
Can I reduce my payments on account?
Yes, if you genuinely expect a lower bill, you can ask HMRC to reduce them online or on form SA303. If your actual bill turns out higher, interest is charged on the shortfall.
The bottom line
Self Assessment punishes delay in stages, and the stages stack: one day late costs £100, while six months late with tax unpaid can cost £1,700 plus interest on a £4,000 bill. File early, budget for payments on account, and talk to HMRC promptly if you cannot pay.
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