Here's what I do:
- print the insert on letter size paper
- trim the page to 6.75" in length.
- punch holes in the left side of the insert
- trim a half inch off the right side of the calendar
- place the insert in your planner; fold the right side over to the left until it nearly touches the rings (or until the fold is lined up with your other inserts)
Because I will be taking it in and out of my planner a lot, I cut slits in the holes to make it easier to pull the pages out and press them back in.