Can I Cancel My Allegiant Flight Without a Penalty? Yes, passengers can cancel their Allegiant flight without incurring a penalty under certain conditions. If you purchase Trip Flex at the time of booking, you can cancel or modify your reservation up to one hour before departure without facing any fees. Trip Flex provides flexibility for uncertain travel plans+1-866-463-2404 .If a passenger cancels their ticket within 24 hours of the time they booked, Allegiant will give them a refund. More than that, the travel date must be at least seven days after the cancellation. If you buy a non-refundable Allegiant Airlines ticket, you can't get an upgrade or a seat with more space.