This set includes all the filters you’ll need for an entire year of filter changes for your Winix air purifier. The true HEPA filter lasts an entire year to capture particles from your indoor air. The carbon pre-filter lasts for three months, which means four filter changes per year. This set includes the four filters you’ll need to last the entire year. No need to worry about remembering to order a new pre-filter every few months! Additionally, each pre-filter has an antimicrobial coating to prevent bacteria growth on the filter.