I check my knuckles if its 30/31 days in a given month. Start counting months on first knuckle while including the depth between knuckles as well. Height means 31, depth means 30.
The thing one does need to remember with the knuckle method is to count the end twice before going back the other way. July and August are both 31. I suppose this isn’t an issue if 2 fists are used, but I was taught to use one, so I could use my finger to track and feel the peaks and valleys.
Thirteen days have November
April, May, and December.
All the rest have thirty nine
except for February when the weather is fine.