02/09/2026
New to Self Assessment for 2025/26? Check whether 5 October 2026 applies to you.
If you need to send a tax return and have not sent one before, HMRC says you must tell them by 5 October after the end of the tax year. Registration is separate from submitting the return and paying any tax due.
Unsure? Check early, and message the Greengrass team if you need help understanding the next step.