Typically, if you have a tiny healthy home, it would take you every 6-12 months to replace your filter. Commonly for families of standard sizes or more, it is recommended that you change your filter every 3 months or 90 days. If you have a cat or dog, it is better if you replace it more frequently, like every 2 months. If you have more than one, then you better replace it every 20-45 days.