In the world of frequent flyer reward programs, the miles you earn don't last forever. With many airlines, if you don't use it, you lose it, though some do allow you to reclaim expired miles. The expiration date on miles varies depending on the airline, but as a general rule, miles don't expire for a year or more after you earn them.
As of May 2015, Delta was the only airline where frequent flyer miles did not expire.
Call or Email Customer Service
Call the customer service line for that airline's frequent flyer program and speak to a representative who can reinstate your miles. Some airlines also let you email customer service to start the process.
Pay a Fee
An airline might allow you to reactivate your expired miles for a fee. For example, as of publication American Airlines lets customers get back expired miles after paying a fee of $200 for 1 to 50,000 miles, $400 for 50,001 to 75,000 miles, and $600 for any miles over 75,000. United's fees range from $50 to $400, while Alaska Air charges $75 to reinstate any number of miles for up to a year after the expiration date.
Reactivated miles often have a new expiration date, so be sure to check so that you don't lose them all over again.
Some airlines only allow you to reinstate miles that expired in a certain time period. United, for example, only allows reactivation of miles expired in the last 18 months.