Missed the 5 October Self Assessment registration deadline — what to do now

 

The 5 October 2026 deadline for telling HMRC you need to complete a Self Assessment return for the 2025/26 tax year (6 April 2025 to 5 April 2026) has now passed. If you were meant to register and missed it, act now: register or reactivate your Self Assessment account on GOV.UK as soon as possible. HMRC warns that telling them after 5 October can lead to a penalty.

 

Late registration does not mean you have lost the year. Once you register, HMRC will send you a letter or email with a different deadline for sending your tax return — normally 3 months from the date on that letter or email. But do not confuse that with the payment date: the payment deadline does not move. Any 2025/26 tax you owe is still due by 31 January 2027, and you will get a penalty if you pay late.

 

Where tax remains unpaid because you never notified HMRC, a failure-to-notify penalty can also apply, so the sooner you register the better. Start at the GOV.UK 'Register for Self Assessment' page, and if you registered in the past, check whether you need to reactivate your account or request a new Unique Taxpayer Reference.