The Allegiant Air cancellation policy is intended to provide flexibility within specific bounds. Unless you selected Trip Flex, a service which offers you more freedom, you may not be entitled for a cash refund if you reschedule a flight in excess of 24 hours after booking. In the absence of Trip Flex, cancellations may result in an Allegiant account credit that can be allocated to future trips. Remember that there's typically an expiration date on this credit. Since the policy is subject to change, it's a good idea to visit Allegiant Air official site to get updated information or get in touch with the customer support.