adding a 3rd box for 2 cats who share?

We have two cats, one of whom is a rescue with a history of anxiety. We currently use two large boxes in different rooms, but the rescue only uses one of them while the other cat uses both. Should I add a third box to see if that helps the rescue feel more secure, or is the current setup fine since they are sharing?

I have already detailed the vet visit and the specific history of Whiskers' anxiety in Whiskers' recent vet check and anxiety management, so I will not repeat that here. I am simply looking for thoughts on the physical setup.

Oh my gosh, Pam, I am so sorry Whiskers is having a hard time! I am always on edge when Coco gets stiff. Since you mentioned the anxiety, have you looked at Signs of stress in cats with anxiety? I think adding a third box is a really good idea! More options usually mean less stress. I definitely added another one for Peanut when he was a kitten and it helped so much!

The general rule of thumb is one box per cat plus one, which is discussed in The rule of N+1 for litter boxes. However, placement is often more critical than quantity. If the two boxes are in quiet, separate areas, the rescue may simply prefer one location due to its scent profile or sightlines. You might want to review Litter box placement tips for multi-cat homes to see if the current locations offer enough separation.

It is interesting how Willow, my senior grey cat, has become quite particular about which box she uses, even though we have three. I think it has to do with the texture of the floor near the box. If Whiskers is deaf, perhaps the vibration of the other cat using the shared box is a factor? I recall reading in Why cats stop using a specific litter box that sensory input plays a big role.

Thank you all. I will check the placement tips. I am leaning toward adding the third box in a hallway that is currently unused, just to give Whiskers a dedicated space that Tux does not frequent. Does anyone think a low-sided box would be better given his age? I know Penny had issues with the edges, as mentioned in Penny's arthritis and litter box height, but Whiskers does not have diagnosed arthritis, only anxiety.