What is the cat to litter box ratio?
As a general rule of thumb, it is good to have one litter box per 1-2 cats, and clean the litter boxes at least once daily.
Has there been anything or anyone new in your house?
Changes such as house guests, a new baby, remodeling, or a new pet can stress your cat. In some cats, this is obvious - hiding or skittish behavior. In other cats, they may not appear outwardly stressed, but may void urine out of the box to show their disapproval -- for example, urinating on your house guest's shoes. Stress and not voiding as often as usual can also lead to a bladder infection.
Feline urinary behavior and medical problems are complex topics. Contact your veterinarian if any changes in litter box habits are noted.
Additional Reading:Urinary Problems in Cats
Help - My Cat is Using the House as his Litter Box
Quick Tip - Shopping For Cat Litter
My cat urinated on the bathroom rug. How can I stop this behavior?
Senior Dementia in Cats
Litter Box Essentials