You must give HM Revenue and Customs (HMRC) specific information about your company within 3 months of starting up in business. You may get a penalty if you don’t.

You can do this online once you have got your company’s Unique Taxpayer Reference (UTR):

https://www.gov.uk/limited-company-formation/set-up-your-company-for-corporation-tax

HMRC will use this information to work out when your company must pay Corporation Tax.

You can also register online with HMRC to notify self-employment using form CWF1:

https://www.gov.uk/government/publications/self-assessment-and-national-insurance-contributions-register-if-youre-a-self-employed-sole-trader-cwf1

You need to register by 5 October following the end of the tax year you need to send a tax return for. If you’re late, you won’t get a penalty as long as you pay your Self-Assessment bill in full by the deadline.