With two adult cats I had two or three litter boxes, scooped each daily. Replace litter approximately weekly.

EDIT: After reading annztoo's post just below, I think I was more like her in that I only did a complete replacement every six weeks or so. I did add litter at least weekly.

The thumb rule I have frequently heard for the number of separate litter boxes is= # of Cats + 1

Two cats means three litter boxes. I went for two until they were senior citizens at which time they tended to poo at the edge or actually outside of the boxes. Went to three boxes and problem disappeared.

EDIT: Added to say, I always kept the litter boxes together. I had up to five adult (English) Bulldogs and sometimes puppies.

Multiple locations for litter boxes wouldn't have worked for my situation.

I can see where you could have an issue with 2 cats using the same box 24/7. Besides them having to share one box, I think their diet and the brand of cat litter you use also plays a part in how often you need to dump the litter and start fresh. I have two adult cats and use an unscented (yet I can detect a slight scent), clumping litter in a total of 3 litter boxes. Each cat tends to choose its favorite box and the 3rd box is occasionally shared. I average around 6-8 weeks before I empty the box and start over.

I make it a habit to keep disinfectant wipes near each box and after scooping I wipe the inside edges of the box with the wipes. I now use A&H and Simple Step brands but find the Simple Step Ultra Multi-Cat to be the best at holding clumps together.

In most cases, placing the extra 2 litter boxes in different (easy to access) rooms works best to prevent any territorial issues, or chances of sneak attacks, when the box is being used.

My young cats are littermates, and share everything. I honestly hadn't considered additional litterboxes, thank you both for your help.

I've never had but one box with up to three cats. I only have one now. I have used World's Best cat litter for years and years. It is much better than the clay litters. With one cat, I only change every two weeks, up to one month. The more cats the more often I changed. The only cat I used clay litter with, died in 1998. I scoop every day. It clumps with the pee and poop, so it stays clean. It may cost more, but is well worth it. I tried the Sweat Scoop (wheat litter) and it is OK, but not as good as World's Best (corn).

Hi - yes, the "formula" is "one for one plus one" - as said above, however many cats you have, then one more. 4 cats = 5 litterboxes, and so on. Of course, it's not a rule .... just advice. My cats (I have 3 cats and 4 litterboxes) like to use different litterboxes for different things .... they don't often use the same box for pee and for poop.

Now - a question. What type of litter are you using? Do you use clay litter or scoopable litter? How often you should likely change the box will differ with your answer.