NOTE Calendars will only show tasks that have a due date

To reduce clutter you can opt to have certain tasks – with due dates – not appear as calendar events.

This is set at Task list level.

Use the “edit” link in each Task list header bar

You will see an option Show these tasks in Calendar?

You are given the option as you create each task list. The default is “Yes”. To turn it off simply untick the box.

(Note: You can change your decision / display at any time by using the task list’s “edit” feature).