English Translation from HMRC Speak: If you have not yet registered for Self Assessment, and have become self employed between 6 April 2021 and 5 April 2022, you must register with HMRC by 5 October 2022 or face penalties.
The deadline for registering for Self Assessment is 5 October after the end of the tax year; anyone who needs to register for 2021-22 now has less than a week left or they will face penalties.
There is an obligation to notify HMRC of chargeability to Income Tax and capital gains tax within six months of the end of the tax year.
If you fail to notify HMRC of your chargeability to tax and have unpaid tax on 1 February 2023, penalties will be due unless you have Reasonable excuse for the failure.
You can register with HMRC for Self Assessment here.