Some flyers are under the impression that logging in to their Frontier account extends the expiration date of their miles.
What really happens is that if you have booked a future flight, the expiration date changes to six months from today and continues to change up to the flight date. If you have no future flights planned, the expiration remains at six months from the last flight you took.
To illustrate this, say that your last flight was on 1/1/15 and you have no future tickets on Frontier. Your expiration should be 7/1/15.
If, on 6/20/15, you purchase a ticket that leaves on 8/1/15 and returns on 8/5/15, your mile expiration date is extended to 12/20/15 (six months from 6/20). If you check your account anytime between 6/20 and 8/5, you'll find that the date is always six months into the future (i.e. between 12/20/15 and 2/5/16). If you check the account on 8/6 or later, you'll find that the date remains at 2/5/16 which six month after your last flight on 8/5/15.
Now, it's possible that the developer of the site was a Schrödinger fan, in which case, your expiration date is in an indeterminate state until and unless you log in to see it
