I created this calendar page where you can specify the number of days into the future you would like calendars for, and it will generate monthly calendars up until that date. The idea is that you can then print them out and cross out the days one by one.
I’m having a little trouble with the page breaks and I don’t think the project is worth the time it would take to do it server-side, as a PDF document.
I may come back to this.
You can view the countdown calendar page here: