I've not had to do this so I was intrigued by your question.
This webpage offers some solutions of sharing a calendar between a Mac and a Windows computer, and has all the steps you need to achieve this.
This page shows three options:
- Outlook on Mac to Outlook on PC
- Use a Gmail account on the Mac Calendar app and on a PC use the Gmail account in Outlook
- Use an iCloud Calendar on a Mac and iCloud for Windows on a PC.
On balance, I'd be trying the Gmail option first as it satisfies both users and has a calendar on their native application, but there is also merit - at least on the Mac side - in having the shared work calendar separate to your private calendars in the Calendar app. This depends on how you use your Calendar of course.
Or perhaps someone else who knows the Windows side a bit better than I do (which is to say hardly at all) can offer a more elegant solution?