Join Date: Mar 2010
Location: Ontario, Canada
I have 2 cats and I formerly had 4 boxes, but moved down to 3 a few months ago. However, I have a large house. I use Maxx Cat, Small Spaces (despite the large house!), because it has virtually no dust, minimal tracking and excellent odor control. However, I don't believe it's sold outside of Canada. My boxes are located in my ensuite bathroom (attached to my bedroom), the dining room (formerly Abby's safe room) and the den (which is the "cats room", since there's nothing in there other than cat toys!).
I think the reason for the "plus one" rule of thumb is to cover the situation where you have cats who like to pee in one box and poop in another. If yours don't bother about that, you should be fine with two. As for what to do when you get a new kitten (I take it that's a new kitten on top of your two existing cats)...well, you will need another litter box initially for the kitten's safe room. Once the kitten has the run of the house, you can see how things go with 2 boxes for all 3 cats. If all three cats get along, there's no litter box "guarding", and you scoop regularly, you might be fine with only 2 boxes.