As a general rule, most airline and hotel programs require some level of activity in your account in order to avoid expiration. These are the main airline and hotel programs that we use, the period of inactivity that will make your miles expire, and what you can do to avoid losing them:
Airlines:
American Airlines: 18 months
Delta: Miles never expire
United: 18 months
U.S. Airways: 18 months
British Airways: 36 months
Southwest: 24 months
Hotels:
SPG: 18 months
Hilton: 12 months
Priority Club: Points never expire
Club Carlson 24 months
Marriott Points never expire
Other programs:
Amex Membership Rewards: Points never expire
Chase Ultimate Rewards: Points never expire
How to avoid losing your hard-earned miles:
The first thing you should do is sign up for AwardWallet, which tracks all your miles and points balances and their expiration dates, and sends you alerts when your miles expiration is approaching. You can find more information on AwardWallet in this article.
If you have points coming up for expiration, there are many things you can do to create activity in your account. For instance, you can simply redeem some points for a free flight or hotel stay, or buy or transfer points into and out of your account. If you do not have any trips planned, by far the easiest and cheapest way to reset the expiration clock on your miles is by using the Dining Rewards Network.