Use double sided calendar cards (or just use single-sided ones, but double sided have more interest), and when it actually reaches that day turn it around.
Okay for whatever reason this has really helped my kids with keeping what day it is straight and they really like turning the card around.
I’ve tried adding in the days as we reach it and since we’re not good about doing calendar every day (how was I so good at it when teaching and not now?) it rather confuses them. This is BRILLIANT! If I do say so myself.