Hey CJ! The HPA300 uses a pre-filter (HRF-AP1) and the True HEPA filter (HRF-R3) is a 3-pack. The Pre-filter should be changed every 3 months and the HEPA filter is recommended to be replaced every 12 months. The frequency will vary based on actual usage of the unit, there is a reminder light that will illuminate to remind you. Thank you!