I honestly think most people know how many days in each month..

But yeah, the point still stands. Having a calendar actively has wrong number of days is very misleading and counterproductive even if one knows how many there are supposed to be. Not to mention it doesn't even have month shown.

For some months like February (unusual), October (Halloween), or December (New Year's Eve) I remember them.

But for the other months I sing the song. Takes about ten seconds, required monthly at most. I think this is pretty common.

Interesting.

I personally just remember the cutoff point (7/8), and before that odd months have 31, after it even months have 31 days. It eventually became "muscle" memory.

For me at least, once I hit my thirties I had just kind of memorized them all by osmosis.

What's wrong with counting on your knuckles for the 12 total times per year that you need to adjust this calendar?