A host of circumstances could explain why your cat might be missing the litter box. Sometimes it's a behavioral problem, but sometimes a health condition may cause your cat to go outside its box. If left unchecked, a health issue, such as a urinary tract infection, can lead to a potentially life-threatening condition for your cat.
An early warning sign that your cat may start pooping outside its box: When a cat that's previously always "covered" its litter box deposits stops doing so, more litter box surprises may follow.
Why Do Cats Poop Outside the Litter Box?
Most often, litter box problems are caused by a change in the cat's routine or issues with its litter box. But if your house-trained cat suddenly stops using its box, your first step is to take your kitty to the vet to rule out any health issues.
Sometimes if your cat has diarrhea or constipation, the urge to go may be sudden and overwhelming, and it may not make it to the litter box in time. This situation should be temporary, however, provided your kitty has no underlying health conditions.
If your vet determines that the issue doesn't have a physiological basis, she'll probably move on to exploring whether your cat has a behavioral problem.
Stress and Behavioral Issues
A sudden change in your kitty's bathroom behavior may be attributed to several different possible causes, many of which boil down to feline stress.
Smelly Litter Box: It's very common for cats to turn up their noses at a litter box if it doesn't meet their exacting standards for cleanliness and odor. If it's not pristine, even cats that have been litter trained for years may reject the box in favor of another area (usually one that will get your attention).
Wrong Box Location: Is the location of the litter box problematic for your cat? If it's near a door or in a part of the house that gets a lot of traffic or that the cat can't easily get to, consider moving it. This isn't recommended if your cat has dementia as it may create more confusion.
Change in Household: If another cat or animal or even a new baby has been introduced to the household or if someone has moved in, moved out, or moved on, your cat may simply be marking its territory. This should be temporary until the cat gets used to the new situation. But be aware that any change to a cat's routine or environment can cause stress, which may result in out-of-the-ordinary behavior.
Recently Adopted Kitty: A cat that's been recently adopted may take a few weeks or months to fully adjust and feel comfortable enough to reveal its personality. It may be that your adoptive cat was feeling a bit uncertain at first and was willing to share the litter box but later changed its mind.
How to Stop Your Cat From Defecating Outside Its Litter Box
In the absence of health issues, take steps to prevent your cat from doing its dirty deeds someplace besides its litter box.
Clean the Box
First and foremost, scoop clumps from the litter box daily and deep clean it frequently. This means jettisoning the old litter, scrubbing the empty box with mild dish soap and warm water, rinsing it with clean water, letting it air-dry, and pouring in a fresh supply of clean, unscented litter (sometimes scented litter is unappealing to finicky cats). Whenever you handle your kitty's litter box, always use rubber gloves and a face mask to protect yourself from microscopic bugs and litter dust.
If you're pregnant, leave all litter box maintenance to another member of the household to reduce your risk of contracting toxoplasmosis.
Focus on Location
If you find that your cat is drawn to using a particular spot, such as a bath mat, as its latrine, try to block its access to the room by setting up a baby gate or closing/locking the door whenever possible. At the same time, encourage your pet to use its litter box as intended by locating the box well away from its food and water bowls in a quiet, private area that's easy to get to.
Add Another Litter Box
If you've added a second cat, consider installing additional litter boxes rather than trying to make both cats share a box. The optimal number of litter boxes is one for each cat plus one more. This means that if you have two cats, you should provide three litter boxes. Note that the boxes need to be in totally different places. Otherwise, one cat may attempt to "guard" and own all the toilets and keep the other cat away.
Put Up Obstacles
If there's a particular area where your cat has been going frequently and you can't block its access, try laying down aluminum foil or spray the area with a kitty-safe deterrent. The goal is to make the inappropriate area as undesirable to the cat as possible.
Re-Create the Scene of the Crime
Take a look at the surface where your cat prefers to defecate and try duplicating that surface in the litter box. For instance, if your kitty likes tile, leave the bottom of the litter box bare. If it targets paper, line the bottom of the box with paper; if it goes on carpeting, install a carpet remnant in its box.
If, in spite of your best efforts, your cat defecates outside the litter box for any reason, thoroughly clean the area with an enzymatic cleaner so your kitty doesn't catch the scent and think it's OK to go there again.