Several users had this request:
I need to add an event to two calendars at once (e.g. my personal calendar and a shared departmental calendar). I'm currently creating the event in the first calendar, then copy and paste it in the second calendar. Is there an easier method?
Possibly. Outlook has a Copy to My Calendar button which will save a couple of steps but it doesn't have an option to duplicate all newly created events to your personal calendar automatically.
To use Copy to My Calendar, create the event on the shared calendar then click the Copy to My Calendar button instead of Save and Close. This creates a copy on your calendar and you'll be asked if you want to save changes to add it to the current calendar. If you click Save (Ctrl+S) before Copy to My Calendar, you'll avoid the save changes dialog.
When the shared calendar is in a mailbox or is a mail-enabled Public Folder, using a meeting request to invite the calendar works, but the event will show up as tentative on the shared calendar. To auto accept, a shared mailbox can be converted to a resource mailbox and auto accept enabled.
If you can use a macro, I have one that will copy events between calendars. The macro and instructions are at Copy New Appointments to Another Calendar using VBA