"Mileage expiration" refers to the point at which the miles or points you have accumulated through a loyalty program or rewards system become invalid or unusable because they have reached their expiration date. Full definition
The airline extends mileage expiration by 18 months from the most recent earning date. (rewardexpert.com)
United and American Airlines are the two major U.S. carriers still clinging to archaic mileage expiration policies. (milenomics.com)
Each year, credit card holders can take a look at mileage expirations, focusing on those airlines whose miles will expire before then next checkup. (creditcards.com)