The calendar we used to have were removed due how little it was used and the place it took up.
To know about contests and other happenings is what the news section and the news update is for which is posted every month around the 1st if not on the 1st.
If you meant as in a more complicated calendar in it's very own page in the tabs for the site for example, it would be much more work than actual reward at current date if it was made.