UK tax return: you must tell HMRC by 5 October or face a penalty for staying quiet

You have until 5 October 2026 to tell HMRC that you need to file a tax return for 2025/26. It applies if, in the last tax year (6 April 2025 to 5 April 2026), you had income that was not taxed automatically: self-employment above £1,000, rent, savings interest, dividends or money from abroad. The return itself comes later — 31 October on paper, 31 January 2027 online — but telling HMRC has to happen now.

What exactly has to be done by 5 October?

Register for Self Assessment on GOV.UK. HMRC puts it plainly: you must tell them by 5 October if you have not sent a tax return before, or if you were registered before but did not need to send one for the 2024 to 2025 tax year. In other words, the 5 October deadline is for newcomers and for people coming back after a gap.

If you filed for last year and keep filing, you do not register again: you already have a UTR, the ten-digit taxpayer reference, and it stays with you.

Who has to file a return at all?

HMRC lists the triggers: you were self-employed as a sole trader and earned more than £1,000 before deducting anything you can claim relief on; you were a partner in a business partnership; you had Capital Gains Tax to pay; you had to pay the High Income Child Benefit Charge and do not pay it through PAYE; you are an off-payroll worker repaying a student or postgraduate loan.

There is a second list — untaxed income: money from renting out property or land, tips and commission, savings interest, dividends, foreign income, and any taxable UK income if you are not a UK resident.

The £1,000 is not a grey area you can stay quiet about: it is the trading allowance, with a separate £1,000 property allowance if you have both kinds of income. Below it you generally do not have to tell HMRC about trading income; above it you either deduct your expenses or take the £1,000 instead of them.

Why does this matter more if you moved to the UK recently?

Because "foreign income" is not just a salary. It is interest on an account in another country, dividends from a company abroad, profit from letting the flat you left behind. UK tax works on a resident's worldwide income, and none of that reaches PAYE by itself — you are the one who reports it.

The second reason concerns recent arrivals. On 6 April 2025 the remittance basis was replaced by the 4-year foreign income and gains regime (FIG). It can free your foreign income from UK tax — but only if you claim it.

What is the 4-year regime, and why does it depend on filing?

You qualify if you are a UK tax resident under the statutory residence test and you are still within your first four years of UK tax residence following at least ten consecutive years as a non-UK resident. The claim is made on your Self Assessment tax return — there is no other route. No return, no relief.

It has a price worth knowing in advance. Claim it and you lose your tax-free allowances for Income Tax and Capital Gains Tax, plus Married Couple's Allowance, Marriage Allowance and Blind Person's Allowance if you were eligible. The foreign income you claim for is also counted in your adjusted net income, which drives Tax-Free Childcare and the High Income Child Benefit Charge.

The years do not roll over: the four run consecutively from the start of your UK residence, and an unused year is simply lost. If you leave the UK and stop being a resident, those years cannot be claimed, but the remaining ones survive your return.

Which deadlines follow 5 October?

A paper return must reach HMRC by 11:59pm on 31 October 2026. An online return is due by 11:59pm on 31 January 2027. The tax for 2025/26 is payable by 31 January 2027 as well.

Two more dates get forgotten. 30 December 2026: if you want a bill of up to £3,000 collected through your tax code, the return has to be in by then. 31 July: the second payment on account towards the following year.

What happens if you are late registering?

Register after 5 October and HMRC will send a letter or email with a different filing deadline — three months from the date on it. The tax is still due by 31 January; that date does not move.

And if you registered after 5 October and have not paid the whole bill by 31 January, a "failure to notify" penalty is added. It is calculated on the tax still left to pay, and it arrives separately, within 12 months of HMRC receiving your return. The penalty is for the silence, not for the paperwork.

What do late filing and late payment cost?

For a late return: £100 straight away, even if no tax is due. After three months, £10 a day up to a maximum of £900. After six months, a further 5% of the tax due or £300, whichever is greater. After twelve months, another 5% or £300.

For late payment: three separate penalties of 5% of the unpaid tax — at 30 days, six months and twelve months — plus interest. HMRC's late payment interest rate is 7.75% from 9 January 2026, set as the Bank of England base rate plus four percentage points.

If a partnership return is late, every partner is charged a penalty, not only the one who filled it in.

What changes if your turnover is above £50,000?

Making Tax Digital for Income Tax started on 6 April 2026 for some sole traders and landlords. It caught those whose qualifying income — turnover from self-employment and property, before expenses — was over £50,000 on the 2024/25 return. HMRC worked this out itself and wrote to the people affected.

The threshold falls in steps: £30,000 on the 2025/26 return means using MTD from 6 April 2027; £20,000 on the 2026/27 return means from 6 April 2028.

In practice it means keeping records in compatible software and sending HMRC four quarterly updates a year — by 7 August, 7 November, 7 February and 7 May. For those already in the system the next one is 7 November 2026. For the first year (2026/27) HMRC says it will not apply penalty points for late quarterly updates, but penalties for a late tax return or late payment still apply.

What should you do now if you have never done this?

First check whether you need to file at all: GOV.UK has a free tool, "Check if you need to send a Self Assessment tax return". Then register — you will need a Government Gateway account.

After registering, HMRC sends your UTR. You cannot file without it and it does not arrive instantly, so leaving this to the last days before 31 January is a bad plan. HMRC's "Check when you can expect a reply" tool shows current waiting times.

If you can already see that paying in full by 31 January will not happen, you can arrange Time to Pay with HMRC in advance. It does not stop interest, but it does stop late payment penalties.

Where can you get help for free?

Straight from the source: HMRC itself (the Self Assessment helpline number is on GOV.UK), free advice from Citizens Advice, and tax charities for people on low incomes. Paid "tax refund agents" who ask for access to your HMRC account and take a cut of the refund are a different matter — nobody needs your Government Gateway login.

And the point about today's date: there are fewer than three weeks left until 5 October. Registering takes minutes; the penalty for staying quiet is calculated on the tax you did not pay.

All upcoming filing deadlines, bank holidays and decision dates are collected in the ONLYWAY calendar, day by day, with explanations.