Inappropriate elimination is a major reason many cats are returned or dropped off at a shelter. And unfortunately, many of these cats are labeled unadoptable and euthanized.
If your cat is not using their litter box, they are trying to tell you something. The first thing you should do is get them seen by a veterinarian to rule out any medical issues. If you get an all clear, then look at your setup.
Make sure you have enough litter boxes. The rule of thumb is one more box than the number of cats. So, if you have 2 cats, you should have 3 litter boxes. And don’t line the boxes up next to each other. Position them throughout your home in out-of-the-way quiet locations.
Next, make sure the litter box is large enough. Many feline behaviorists state a litter box should be 1.5 times the length of your cat. Most commercially available litter boxes are too small for the average adult cat. Consider instead storage totes designed to fit under a bed. A potential issue with these is the inside bottom is not smooth. If that is an issue, consider a concrete mixing tub available at a hardware store. Your cat will probably be happier, and because you are out of the “pet department”, your new “litter box” will probably be cheaper than a conventional litter box.
Then, make sure you scoop/clean the box regularly, at least daily.
Just remember, if you have a cat with arthritis or a kitten, get a box that has one low side so the cat or kitten can easily get in.
Read “The Size of Your Cat’s Litter Box” to learn more about the appropriate size of a litter box.