Below you will find instructions on how to add your Outlook Calendar to Microsoft Teams.
STEP 1: Click “+” icon under the channel you want to add the calendar to, and then select Website.
STEP 2: Type the name of the tab as you like and paste the following link under URL tab. https://outlook.live.com/calendar/view/month (if you are using office 365 account paste the link: https://outlook.office.com/calendar/view/month)
If it asks you for you account credentials, log in using them and then you will be able to view the calendar within Microsoft Teams.