The deadline for an online Self Assessment tax return for 2025/26 is 11:59pm on 31 January 2027, and the tax owed must be paid by the same date. Paper returns were due earlier, by 31 October 2026. Filing late costs an automatic £100, and further penalties follow after 3, 6 and 12 months.
Those are the two dates most people need. The Self Assessment year has several others, though: a registration deadline, a cut-off for paying through your tax code, and a second payment on account in July. Here they all are for the 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026.
Self Assessment deadlines for 2025/26
| Date | What is due |
|---|---|
| 5 October 2026 | Register for Self Assessment if you have not filed before, or did not need to file for 2024/25 |
| 31 October 2026 | Paper tax return (SA100) must reach HMRC |
| 30 December 2026 | Online return, if you want a bill under £3,000 collected through your PAYE tax code |
| 31 January 2027 | Online return; balancing payment for 2025/26; first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
| 31 January 2028 | Last day to amend a 2025/26 return (12 months after the filing deadline) |
Two of these dates have already passed. If you missed the 5 October registration deadline, register now. HMRC will then give you a filing deadline 3 months from the date of its notice, but the tax is still due by 31 January 2027. Our guide to registering for Self Assessment covers the process. If you missed the 31 October deadline for a paper return, you can still file online by 31 January without a penalty, because the law sets separate deadlines for paper and electronic returns.
The paper tax return deadline
A paper return must reach HMRC by 31 October, not just be posted by then. Some people have to file on paper. Trustees of registered pension schemes and non-resident companies cannot file online, and their paper return is due by 31 January 2027. A partnership with a company as a partner and an accounting date between 1 February and 5 April has its own deadlines: 9 months from the accounting date on paper, or 12 months online. Our SA100 guide explains which supplementary pages you need.
Paying through your tax code: 30 December
If you are employed or receive a pension, HMRC can collect a Self Assessment bill through your tax code over the following year instead of taking it as a lump sum. You qualify if all of these apply:
- Size of bill. You owe less than £3,000, and you cannot make a part payment to get under this limit;
- Existing PAYE. You already pay tax through PAYE;
- Timing. You file on paper by 31 October or online by 30 December.
Payments on account: 31 January and 31 July
Unless your last bill was under £1,000, or more than 80% of your tax was collected at source, you also make two advance payments towards the next year's bill. Each is half of the previous year's liability, and they are due on 31 January and 31 July. This is why many people's January 2027 payment covers two things: the 2025/26 balancing payment and the first instalment towards 2026/27. Our guide to the 31 July deadline explains the second payment, including how to reduce it if your income has fallen.
Penalties for missing the deadline
| Late filing | Penalty |
|---|---|
| 1 day late | £100 |
| 3 months late | £10 a day, up to £900 |
| 6 months late | 5% of the tax due or £300, whichever is greater |
| 12 months late | Another 5% or £300, whichever is greater |
Paying late is penalised separately: 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest on everything outstanding. If you notify HMRC late and do not pay in full by 31 January, you may also get a failure-to-notify penalty. Current interest rates are listed in our guide to HMRC interest rates.
Worked example
Priya owes £4,000 for 2025/26. She files and pays on 31 August 2027, seven months late. Her filing penalties are £100, plus the maximum £900 in daily penalties, plus £300 at six months, because 5% of £4,000 is only £200. That makes £1,300. Her late payment penalties are 5% at 30 days and 5% at six months, £400 in total. The total is £1,700 in penalties plus interest, on a £4,000 bill. Filing on time, even without paying, would have saved her £1,300.
If you have a reasonable excuse, you can appeal against a penalty. Penalties must be paid within 30 days of the notice.
What Budget 2026 changes
None of the 2025/26 dates move. Budget 2026 announced three changes, not yet law, that will affect Self Assessment later:
- Trading allowance. From 6 April 2027, the allowance and the Self Assessment reporting threshold for trading income both rise from £1,000 to £3,000;
- Employment expenses. From 6 April 2028, the £2,500 threshold that sends employment expense claims through Self Assessment will be removed, so more claims will go through PAYE;
- Payments on account. From April 2029, after consultation, taxpayers who make payments on account will pay smaller amounts more often during the year, instead of two large instalments.
Our Self Assessment calculator gives an estimate of your bill before you file. If you would rather not deal with January yourself, our Self Assessment team prepares and files returns well before the deadline, and our income tax returns service covers more complex cases such as property income, foreign income and capital gains.