1. A method for determining a remaining useful life of an air filter, the method comprising the steps of: measuring a first airflow rate and a first air pressure (P 1 ) in an air cleaner assembly downstream of the air filter, P 1 corresponding to the first airflow rate; measuring a second airflow rate and a second air pressure (P 2 ) in the air cleaner assembly downstream of the air filter, P 2 corresponding to the second airflow rate; obtaining pressure differentials across a new air filter at the first airflow rate (A 1 ), across the new air filter at the second airflow rate (A 2 ), across an end-of-life air filter at the first airflow rate (B 1 ) and across the end-of-life air filter at the second airflow rate (B 2 ) from a data storage device; calculating with a processor a result indicative of a useful life remaining for the air filter by taking into account P 1 , P 2 , A 1 , A 2 , B 1 , and B 2 ; and reporting the result to a user.