The biggest complaint of cat owners is due to having a cat that suddenly decides he doesn’t want to eliminate in his litter box.
Besides the smell, there is the added cost of ruined rugs and the embarrassment when visitors stop by. Cats are, however, naturally clean animals and you will need to do some investigating to see what is going on that may have changed this habit.
The first reason cats stop using their litter box is cleanliness. How often do you clean the box? While one cat may tolerate once a day, others may insist the box be cleaned each time they use it. In the latter case, it might help if you can invest in a self-cleaning litter box. If cost is an issue, then try cleaning the box more often and see if this helps.
Have you recently changed litter brands? Most cats prefer the brand they are used to. This doesn’t have to be the most expensive; some actually prefer the cheaper brands. If you find a litter that seems to make your cat happy, stick with it.
A more important reason a cat may stop using his litter box is illness. A visit to the vet to have your cat checked for possible urinary track infection could be in order. A cat with this infection may feel pain upon elimination and associate that pain with the litter box.
Keeping in mind that most cats will not stop using a litter box once trained should make it easier for you to understand. Find the cause by eliminating things one by one. Both you and your cat will be happier for the effort. He stays out of trouble and you benefit by a cleaner-smelling house and nice carpet.