How often(change air filter)

How often should i change my air filter? I heard 20,000 miles btu i wanted some more opinions thanks..

Don't know the actual factory rec's. but I try to do mine every 6000 (every other oil change). Might be overkill, but I don't want to have to worry about a dirty filter causing poor performance or milage. Especially since they don't cost much.

I do like MadCat455, every other oil change, [@ 6,000 mi.] it's worth the $$ to change often. I also change more often if needed depending on driving conditions. If I end up doing a lot of driving in a dusty area or say this spring when all of the salt and cinders are being crushed into dust I'll check the filter once a week to make sure it's still clean. I also keep a couple of extras one in the car and one in the garage. 20,000 seems too long to wait to me, your choice.