Most filters have a recommended guideline on the box or plastic. It may say “Lasts up to 3 months” or “Change filter every 90 days”. Look around at the store and you’ll notice that some are meant to only last a month, while other manufacturers (like Honeywell) have produced media air cleaners with filters meant to be swapped once every 6-12 months. The norm seems to be once every 3 months for most higher quality filters, but we have a rule of thumb that we tell our friends and family to go by. If they’re dirty, change them! A dirty air filter can contribute or cause damage to pricey components, like your compressor, so it’s better to change it out more often than to let it go. If you want to follow the manufacturer’s recommended limit, we suggest writing the date on the filter when you swap it out, and setting a reminder for yourself in your phone or on a calendar. Also note that your filter manufacturer might have a different recommendation from your HVAC equipment manufacturer.