Q: How long do miles last before they expire?
A: The current industry standard is to allow miles to remain in a member's account forever as long as there is some activity every 36 months. Since account activity includes any earning or redemption, miles are effectively eternal.
Among the U.S. airlines we cover, Southwest is the exception, expiring Rapid Reward credits 12 months from the date they are earned. Other low-cost carriers have similar policies. Hotel and other loyalty programs generally do not have expiration dates.
It is best to contact your specific program to find out whether your credits will expire, and if so, when.