Are you excited to explore Frontier and fly with it? Always remember to check out the essential details of Frontier Airlines check-in policy and fees. The next question after buying a ticket is, “How do I complete the check-in process?” Frontier Airlines has multiple options for passengers to check in. You can always use Frontier online check-in as it is easy and starts 24 hours before the flight departure, and offline check-in counters open 3 hours before the scheduled departure.