In the morning once a day usually. I have two cats and had two litter boxes until recently. I had them side by side but Andy would go in one and toss so much litter out of the box in his attempts to cover, that a lot of litter would go on the floor in between them even though there was only a tiny crack. Last week I bought one of those "under the bed" plastic storage thingies and that is now their new litter box. It is just about the size of two litter boxes and works so nice and has such a slippery bottom that my scooper just glides through it! Their box is under the stairs in the basement so I never notice any odor.