Calendar

Calendar
 

-This is an important exam. Students ought to put it (=the date of it) __ the calendar.

Are in and on both correct, and do they mean the same?

Both in and on are correct, but I detect a difference. To me, 'in' implies entering data into an electronic calendar while 'on' implies writing on a printed calendar. Nevertheless, both can be used and the difference in meaning that I've described can be mostly ignored.

Excellent answer. Thank you.