First off, welcome to FT, BXIAN, from an old Mt. Laurel native (grew up in Ramblewood)! Are you new to the area or a long-time denizen?

Most of the airlines have miles expiring in 36 months from date of last account activity (I don't fly US so don't know their policy). AA is nice enough to give you the expiration date up front when you log in to the AAdvantage web site ... most of the other airlines don't offer this. You can always call the 800 numbers associated with each program and get the expiration date of your miles.

Also, BTW, "account activity" for every domestic major airline refers to anything which adds or subtracts miles ... hotel or car rental partner bonus, airline CC activity, redemption, etc.

Southwest is the only exception. Any "credits" you earn disappear exactly one year from when they're earned ... so if you earned 4 credits last December, 10 this year, and 2 next January, your account would show a balance of 12, not 16 (and you wouldn't get the free ticket!)

As for Starwood, they'll freeze your account in 12 months and delete it in 18 w/o any activity; Hilton will put you "on notice" after 12 months and delete you after 15; for Marriott, you're gone after 24 months. Again, this refers to a lack of any activity whatsoever -- if you go to the specific web sites for the programs, there's a million ways to earn miles for each.

You can get more specific info on each program at the boards dedicated to the program. I recommend the Starwood board in particular ...

Hope this helps.

SP