This varies on how often you run the Roomba, kids, pets, carpet, and lifestyle in general. You'll want to check the filters at least 1-2 times a month to check in on how the filter health. I replace the Roomba filter about every 3 months or so depending on how much I use it. iRobot recommends replacing the filter every 2 months, but I've been good with every 3-4 months. When you clean your filters, you'll see when you need to replace it. Don't wait just because it hasn't been a certain time that's passed.