An old picture frame + paint colour sample chips = an inexpensive, reusable monthly (or weekly) calendar. Taking inspiration from the Pinterest community, The Aesthetic Writer made this decorative dry erase calendar.
You need 35 chips, a 12" x 16" frame, and a dry erase marker to create your own version.
Other alternatives have been "pinned" at Pinterest, including this weekly variation (with good binder clip usage).
If you're a colour lover, this DIY calendar is for you.
DIY: Dry-Erase Calendar [The Aesthetic Writer]