Cat just started pooping on the carpet?

It's possible your cat is constipated. That's what mine will do when she doesn't feel well: she can't go in her box, but when she steps out of it she'll eventually release wherever she is. (I learned this by watching her.) (She's 15, btw.) She does have a few favorite spots, and I have learned to put plastic (cheap garbage bags) down in those spots. Anyway, call your vet and ask what s/he recommends for a constipated kitty. You can buy a cat laxative (tuna-flavored petroleum jelly) and it will help.

Good luck with your baby. I doubt if she's forgetting where the boxes are. I think she's constipated.

Edit: it is NOT TRUE that one year in a cat's age equals seven human years; that's bullsh!t. Cats age differently than dogs and people. Certainly yours is very elderly, but my vet says my indoor cat could live for 20 years. But do talk to your vet and follow the vet's advice.

Edit#2: the fact that she has gone two days without an accident is not the issue. Has she had a bowel movement during that time in her box? Has she not had a movement AT ALL? Please give this info to the vet, whether you're happy or not. And DON"T give the poor thing any human laxatives!

If all 3 cats are using the same litter box then that would be a possible reason. Cat's are funny like that if they can smell another cat has been present. Putting him in a cage is not going to help at all. You need a 2nd litter box and both should be cleaned out daily and regularly as some cats won't use one that is dirty.

She’s 18! That makes her 126 in animal years.

It may just be a bowl control issue from being old – my grandma’s geriatric dog had that problem the last couple of years he was alive. But it may also be her way of telling you she’s sick. We found out my cat has a chronic condition that can be controlled with the right food after he pooped on the carpet. He just wanted us to know he couldn’t go #1.

Certainly take her to the vet for a full check-up.

I hate to say it but I would attribute this behavior to old age and wouldn't expect it change. Just like humans, when cats get old, they lose their faculties. She may be forgetting where the box is, she may have lost bowel control so she cant control when/where she goes. I think kitty Alzheimers may be setting in.

When cats get old they sometimes start having incontinence issues, just like humans.