Tell HMRC by 5 October that you need to file a tax return

The next tax deadline in Britain is not January, as most people remember it, but 5 October. By that date you have to tell HMRC that you had income in the past tax year that you are required to report. That year ran from 6 April 2025 to 5 April 2026.

The date applies to people filing for the first time, and to anyone who filed once, did not file for last year and came out of the system. If you filed a return a year ago as well, you do not register again — your first deadline is the October one for paper returns.

Who this is for

GOV.UK sets the cases out plainly. You must send a return if, in the last tax year, you:

• worked for yourself as a sole trader and earned more than £1,000 — before taking off anything you can claim tax relief on;
• were a partner in a business partnership;
• had to pay Capital Gains Tax after selling or otherwise disposing of something that had gone up in value;
• had to pay the High Income Child Benefit Charge and do not pay it through PAYE;
• are an off-payroll worker repaying a student or postgraduate loan.

Then there is income that was never taxed at source: rent from property or land, tips and commission, savings interest, dividends and investment income, foreign income, and any taxable UK income if you are not a UK resident. There is no single all-or-nothing threshold here — check your own position rather than someone's summary of it.

You can also file voluntarily: to prove you are self-employed, to pay voluntary National Insurance contributions, or to claim certain reliefs. Nothing stops you filing when you are not obliged to.

Every date worth keeping

• 5 October 2026 — tell HMRC you need to report, that is, register for Self Assessment.
• 31 October 2026, 11:59pm — the deadline if you file on paper.
• 30 December 2026, 11:59pm — file by this date if you want the tax collected gradually through your tax code.
• 31 January 2027, 11:59pm — the online return, and payment of the 2025–26 tax.
• 31 July — the second payment on account, if you make them.

Trustees and non-resident companies cannot file online: their paper return is due by 31 January 2027.

If 5 October has already gone

The obligation does not go away. HMRC will register you later and normally allows three months from the date of the notice to send the return itself. The payment date does not move with it: the tax is still due by 31 January 2027. Registering late also carries a risk of a failure-to-notify penalty, so there is nothing to gain by waiting.

What lateness costs

Late filing penalties come in steps and stack up:

• £100 immediately, even if you owe no tax at all;
• 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, whichever is greater.

Paying late is charged separately: 5% of the unpaid tax at 30 days, again at six months and again at twelve, plus interest for the whole period. A penalty on a notice must be paid within 30 days of the date on it.

What to do this week

You register on GOV.UK, at Register for Self Assessment. If you were in the system before, you reactivate the account in the same place. HMRC sends back a UTR — the personal tax reference you cannot file without. It does not arrive instantly, which is the main reason not to leave registration to the last day.

While you wait for it, gather what January will need anyway: business account statements, invoices and receipts for expenses, P60 or P45 forms, tenancy agreements and interest certificates from your bank. Sorting that out in September takes an evening; in January it takes a weekend.

Our tools page works out VAT, take-home pay and currency conversions. We do not give individual tax advice: for anything complicated, speak to an accountant or a tax adviser.