Number of litterboxes

This question is addressed to people with more than 1 cat!
I follow the rule of one litterbox per cat, but I heard that it is now one per cat plus 1 extra. Then recently I find out that it is one per cat per level of the house (like if you live in a 2 level house and you have 2 cats it's a total of 4 litterboxes). So could anyone tell me which is which? Thanks!

I find it is best to have at least one litterbox per cat. If you have a lot of cats, like I do, I have a lot of boxes, not really litterboxes, I use large plastic tubs.

I usually say however many cats you have in your house plus 1 under 6 cats. If you are over 6 cats then however many kitties plus 2 trays. If your kitties are allowed outside, they will probably prefer to do their business out there so this rule isnt so strict then. I have 7 cats and 6 trays as I most of mine prefer to go outside. Its great fun doing the pooper scoop every few days NOT!!

I have 2 cats and 2 boxes. I had 3 boxes for a while, but it was a bit overwhelming for a one bedroom apartment.

Well Im breaking that rule I guess
I have 3 cats and 2 boxes, 1 on each floor of my house.
I scoop every day and do a complete cleaning once a week for each box. They seem to do just fine with the way it is, and since Im not one to make more work for myself, I leave it alone

I have 2 cats and 2 boxes. However, Zoey only uses the main litterbox.. the one she's always used. Saki will use both. But Zoey occasionally goes to his litterbox and re-arranges the litter for him

We have a box in the attic, one in the computer room (it started out as Osiris' box, but now they all use it!) and 15 in the basement, all lined up!

I have 6 cats and 4 boxes. They mostly use only 2 of them so I don't think it would make a difference if I had more boxes.

Thank you everyone! I've had my cats for years now and I should know their needs by now. But I get worried when I hear new things on cat care and I may be doing something wrong. Thank you again!