Establishing a connection between Toggl and your personal calendar will make these things possible:
Show calendar events inside Toggl.
Display time entries from Toggl inside your calendar.
Displaying calendar events inside Toggl
Viewing external calendar events is available via the Toggl Calendar view. The Calendar view integration currently works with:
Google Calendar. Available on all plans, including the Free plan. Click here for setup instructions.
Outlook Calendar. Available only on paid plans (Starter and Premium). Click here for more information.
Adding time entries to your own calendar
This can be done by enabling the iCalendar integration (available on paid plans). Once enabled, recent time entries will start appearing inside your personal Calendar. iCalendar integration works with most commonly used calendars (Google, Apple, Yahoo, etc). Open this article for detailed setup instructions.