The lifetime of the filter depends on the level of airborne particles it is filtering with each wear. With general use our filters will therefore last 40 hours and we recommend changing them once every week.With heavy use our filters will require more regular changes - up to every day for very heavy use. We sell our filters in handy 4packs or 8 packs -- for each one month or two month's usage at a time.We also have discounts for subscribing -- 15% -- and for frontline and healthcare workers that may need many more filters with heavier usage. If you fall into the latter category, get in touch with our customer friend team on hello@hllofriend.com for your discount code. You can opt in for a filter subscription when adding your mask to your cart, or adding a filter to your cart.