If you haven't flown much recently but have miles sitting in a frequent flier account, they could vanish before your eyes.
Back when frequent flier programs began in the 1980s, miles either never expired or had a shelf-life of at least three years.
Today, however, airlines put tighter limits on the lifespan of your hard-earned miles, and expiration policies vary by airline.
Should you find your balance suddenly showing zero, don't panic.
Many airlines offer the ability to reinstate expired miles for a fee. (Read more: How to Quickly Rack Up Frequent Flier Miles)
Here's a breakdown of U.S. airline policies on mileage expiration and how to get them back or extend their life.
AirTran: Points in AirTran's A+ Rewards program expire one year after their posting date. Members can extend the life of the credits by one year for $29 each (plus tax), but cannot buy them back after expiration.
Alaska Airlines: Mileage accrued in Alaska's Mileage Plan program are subject to expiration after two years of account inactivity. Deleted mileage can be reinstated for a $75 fee for up to one year.
American Airlines: Miles earned in the AAdvantage program expire after 18 months of inactivity. Miles that expired on or after December 31, 2002 are eligible for reactivation at a rate of $200-$600 (plus tax), depending on the number of miles reactivated.
Delta:Delta bucks the industry and is the only major U.S. airline without a mileage expiration policy. However, the airline reserves the right to close a member's account if repeated communication attempts to a member go unanswered.
JetBlue: Points don't expire as long as you earn points by flying JetBlue or using the JetBlue Card from American Expresson eligible purchases at least once in a 12-month period. JetBlue does not offer a program to reinstate expired points.
Southwest: Points in Southwest's Rapid Rewards program don’t expire as long as you have flight or partner earning activity every 24 months. Southwest does not offer a program to reinstate expired points.
United: Miles in United's MileagePlus program expire after 18 months of inactivity. Miles may be reinstated within 18 months following expiration for $50-$400, depending on the amount of miles reactivated.
US Airways: Miles are subject to forfeiture if no miles have been earned or redeemed within a consecutive 18-month period. US Airways charges between $10-$400 to reinstate expired Dividend Miles for an additional 18 months. If you do not reinstate forfeited miles within 36 months of the last activity date, they will be permanently deleted.
Coming soon on Road Warrior, I'll provide inexpensive tips to avoid mileage expiration in the first place — some as cheap as $2.
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