I rarely do a complete change. In the past year - maybe 3 or 4 times? I use Fresh Step and Scoop several times per day and honestly - I do not think there is any smell! Anything "deposited" is removed. The few times I did a complete change was when I was running low on litter anyway so figure why not? Then, I scrub the boxes with scouring powder plus bleach and rinse really well.

This has been with three cats and three boxes. Now I have five cats and three boxes but one of the boxes is HUGE (my sandy beach) and holds 21 pounds of litter replaced three of my extra large boxes - it is the size of a footlocker It is a plastic storage box that is something a person might store bedding or blankets in and is very tall - sure has cut out the piles of litter on the floor