Tax return UK 2026: who has to file for 2025/26, every deadline from 5 October to 31 January, and what the penalties actually cost if you miss them.
Every January a few million people discover they were supposed to be in the Self Assessment system and nobody told them. HMRC does not usually write to say “you now need to file”. The obligation is yours to spot, and the penalty for missing it starts at £100 whether or not you owe a penny of tax.
So here is the tax return UK position for 2026, in the order you actually need it: whether you have to file at all, the dates that apply to the 2025/26 return, and what it costs when the dates slip.
Self Assessment is not a separate tax. It is the reporting system HMRC uses to collect income tax on money that was not already taxed before it reached you. If everything you earn goes through PAYE and your tax code is right, the system never needs to hear from you.
The trigger is not “did I earn a lot”. It is “was some of my income untaxed at source, or did a specific rule catch me”.
GOV.UK lists five circumstances where a return is mandatory if any of them applied during the tax year that ran from 6 April 2025 to 5 April 2026.
That last one catches contractors out constantly. You can be inside IR35, taxed at source like an employee, and still owe HMRC a return purely because of the student loan.
Beyond the mandatory five, you may also need to file if you had untaxed income of any kind. GOV.UK names money from renting out property or land, tips and commission, savings interest, dividends including investments, foreign income, and any taxable UK income if you are non-resident.
The single most misread rule on the list. The sole trader test is more than £1,000 before expenses, not more than £1,000 of profit.
Worked example. You sell handmade prints on Etsy. Sales of £1,400 across the year, £600 spent on materials, postage and fees. Your profit is £800, which is under a thousand, so it feels safe. It is not. Your income was £1,400, you are over the line, and a return is due.
There is a separate £1,000 trading allowance you can set against that income instead of claiming actual expenses, which in this example would leave £400 taxable rather than £800. Either way, you file.
The government has announced an intention to raise the Self Assessment reporting threshold for trading income from £1,000 to £3,000 gross, which HMRC estimates would take around 300,000 people out of returns entirely. It is not in force. For the 2025/26 return the line is still £1,000.
Filing voluntarily is sometimes the point. GOV.UK lists three reasons people do it: to prove you are self-employed, for instance to claim Tax-Free Childcare or Maternity Allowance, to pay voluntary National Insurance contributions, and to claim income tax relief on maintenance payments.
There is a fourth practical reason. Mortgage lenders want an SA302 tax calculation, and you cannot produce one for a year you never filed.
If none of this settles it, HMRC runs a checker tool that walks through the tests in a couple of minutes.
| Date | What it is |
|---|---|
| 5 October 2026 | Register for Self Assessment if you have never filed, or did not need to file for 2024/25 |
| 31 October 2026 | Paper returns must reach HMRC by 11:59pm |
| 30 December 2026 | File online by 11:59pm if you want the bill collected through your tax code |
| 31 January 2027 | Online returns due by 11:59pm, and the tax itself due by 11:59pm |
| 31 July 2027 | Second payment on account, if you make them |
Two of those deserve more than a row in a table.
5 October is the one people have never heard of. It is not a filing deadline, it is a notification deadline, and it applies the first time you fall into Self Assessment. Miss it and you may get a “failure to notify” penalty, which is based on the amount of tax still left to pay and can arrive up to twelve months after HMRC receives your return.
If you register late, HMRC will write or email with a revised filing deadline of three months from the date on that letter. The payment deadline does not move. The tax is still due by 11:59pm on 31 January 2027 whatever your filing date says.
30 December is the quiet win. File online by then, owe less than £3,000, and you can ask HMRC to collect the bill through next year’s tax code instead of demanding it in one lump. Miss it and you pay another way.
There are two separate penalty regimes and they stack. Filing late and paying late are punished independently.
Late filing:
Late payment: 5% of the tax still unpaid at 30 days, again at 6 months, and again at 12 months. Interest runs on the balance throughout.
Worked example. You owe £2,000 for 2025/26 and you file and pay seven months late, in late August 2027.
That is £1,500 of penalties on a £2,000 bill, before interest, and £1,300 of it is for filing rather than for owing. Filing on time and paying late is a far cheaper mistake than the reverse. If the money is not there, file anyway and then arrange a Time to Pay plan.
Penalties are payable within 30 days of the notice, and you can appeal if you have a reasonable excuse.
Register at GOV.UK. You will need a Government Gateway account, and HMRC issues a ten digit Unique Taxpayer Reference, your UTR, which arrives by post in roughly two weeks. You cannot file without it, which is the real reason late registration causes problems: the clock you are fighting is the postal one, not the filing one.
If this is your first return, our first-time Self Assessment walkthrough covers the form section by section, and the HMRC Self Assessment guide covers how the bill is worked out.
Changed: nothing material in who has to file. The £3,000 reporting threshold has been announced but has not arrived.
Not changed, and worth noting: the personal allowance is still £12,570 and the higher rate threshold still £50,270 for 2026/27, both frozen. Class 4 National Insurance on self-employed profit is 6% between £12,570 and £50,270 and 2% above. Class 2 is treated as paid once profits reach £7,105, so most sole traders pay nothing for it, and the voluntary rate below that level is £3.65 a week.
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You must file if, in the 2025/26 tax year, you were a sole trader earning more than £1,000 before expenses, a partner in a partnership, liable for Capital Gains Tax, liable for the High Income Child Benefit Charge outside PAYE, or an off-payroll worker repaying a student loan. Untaxed income such as rent, tips, savings interest, dividends or foreign income can also pull you in.
For the 2025/26 tax year, register by 5 October 2026 if you have never filed before. Paper returns are due by 11:59pm on 31 October 2026. Online returns and the payment itself are both due by 11:59pm on 31 January 2027. If you want the bill collected through your tax code, file by 30 December 2026.
You get an automatic £100 penalty even if you owe nothing. After three months HMRC adds £10 a day up to a maximum of £900. At six months there is a further charge of 5% of the tax due or £300, whichever is greater, and the same again at twelve months. Late payment carries separate penalties plus interest.
Turnover. GOV.UK says you must file if you earned more than £1,000 before taking off anything you can claim tax relief on. So £1,400 of Etsy sales with £600 of costs is £800 of profit but £1,400 of income, and it crosses the line.
Want to see your actual take-home pay?
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A note on financial advice: NetPay UK calculates take-home pay based on official HMRC tax rules. This article reflects rules in force at the time of publication (19 September 2026). Tax rules change. For complex situations, consult a qualified UK accountant or visit gov.uk/income-tax.
