Once iCloud contacts & calendars are setup correctly, they will seemlessly sync with iCloud.com. I found the following articles that may provide assistance if the information is not syncing correctly to iCloud.com:
- Make sure there are no current issues listed on the System Status that affect iCloud Calendar. The System Status is located on the iCloud Support webpage.
- Make sure you have fully enabled iCloud Calendar for the client you are using (for more setup and troubleshooting information on iOS, OS X, Windows and iCloud.com, see the additional details below).
- Check to see if the issue you are seeing is covered in iCloud Help. To search iCloud Help, visit help.apple.com/icloud.
- Check your settings and preferences as something may not be set up correctly. For example, having incorrect date and time settings can cause issues which are easily resolved by entering the appropriate settings.