What I can think of, needs too many conditions to get that number right for each month.
But check this face, @akar.zaephyr has done something similar (just omited that part ).
I’ve tried tackling this problem but gave up.
There is no tag returning maximum number of days in previous month so there is nothing to base the calculations on.
I’ve simply created a series of squares obscuring the value when it’s below or equal to zero, like below: