UK Self Assessment: Does the 5 October Deadline Apply?

People who first need to complete a UK Self Assessment return for the 2025–26 tax year should generally tell HM Revenue & Customs by 5 October 2026. With that registration deadline approaching, potential first-time filers should check whether they need a return, identify the correct registration route and allow time to receive their Unique Taxpayer Reference.

By the AtheneNet Money Desk

Who should check whether they need Self Assessment

Self-employment is a common reason for filing, but it is not the only one. A return may also be required in circumstances involving income from property, savings, investments, overseas sources or other untaxed income. Some people may need to report Capital Gains Tax matters or repay part of the High Income Child Benefit Charge.

However, receiving extra income does not automatically mean that a return is required. The amount, source and whether tax has already been collected can affect the position. Use HMRC’s official eligibility checker rather than assuming that every side income creates a filing obligation.

Registration, filing and payment are separate tasks

The 5 October date is generally the deadline for notifying HMRC that a return is needed for the previous tax year. It is not normally the deadline for submitting that return or paying the resulting tax.

For the 2025–26 tax year, the main dates are:

• 5 October 2026: notify HMRC if Self Assessment is required and registration is needed.
• 31 October 2026: deadline for a paper tax return.
• 31 January 2027: deadline for an online return and payment of tax due.

Different rules or additional payment dates can apply in some circumstances. Confirm the dates relevant to your own tax year on HMRC’s Self Assessment deadlines page.

How first-time filers can register

1. Check whether a return is required using HMRC’s online tool.
2. Confirm the relevant tax year; the approaching 5 October 2026 deadline concerns the tax year ending 5 April 2026.
3. Follow the appropriate route on the official registration service. The process differs for self-employed people and those registering for another reason.
4. Keep confirmation details and wait for HMRC to issue the information needed to use Self Assessment, including a Unique Taxpayer Reference where applicable. Delivery is not necessarily immediate.
5. Set reminders for the separate return and payment deadlines.

Records worth gathering now

Prepare records that support the income, expenses and tax position being reported. Depending on the circumstances, these could include invoices, business expense receipts, property income records, bank interest statements, dividend information, pension documents, employment records and details of relevant gains.

This is general administrative guidance, not individual tax advice. Anyone uncertain about unusual circumstances should check the official HMRC guidance or seek qualified professional advice before the relevant deadline.

Source: GOV.UK / HM Revenue & Customs