The N+1 Rule, and Why One Box Always Fails
Veterinary behaviourists recommend one litter box per cat, plus one extra. This is called the N+1 rule, and it exists because cats are hardwired to treat elimination sites as territorial resources. A 2019 review in the Journal of Feline Medicine and Surgery confirmed that multi-cat households with too few boxes show significantly higher rates of inappropriate elimination, but the rule applies to single-cat homes too. One box fills up, smells wrong by afternoon, and the cat walks away from it.
