An air filter's lifespan depends on a few factors, such as the type of filter, the size of your home, the number of people in your household, and whether or not you have pets. The average air filter should be replaced every 3 months. However, if you have a larger home or more people in your household, you may need to replace your air filter more frequently. If you have pets, their fur can clog up an air filter faster than if you don't have any pets.