• Before making a reservation at any airline, it is recommended that you educate yourself regarding ticket cancellation and changes policy. It's better to know in advance how much a ticket change or cancellation will cost you, in case you change your mind or in case of an unexpected event in your life. It takes a bit of your time, but it can save you money. Cancellation and changes policies depend on many factors (like: cancellation date, ticket class, destination, if the ticket was paid for, or purchased with award miles, and so on). Keep in mind that most low fare tickets are usually nonrefundable.
• But, even the nonrefundable tickets have a 24-hour cancellation window. The U.S. Department of Transportation requires "each U.S. and foreign air carrier that has a website marketed to U.S. consumers" to allow customers to cancel their reservations within 24 hours without a fee or to hold a reservation for 24 hours without payment, if the reservation is made seven days or more prior to the flight scheduled departure time. You are entitled to a refund in the original form of payment.
• Book directly with the airline, as much as possible. The DOT "24-hrs rule" applies to carriers only, not travel agencies or 3rd party vendors.  Some travel agencies follow the 24-hrs rule for some of their bookings, but if you use a travel agency make sure you check their cancellation policy before you book.
• Also, a nonrefundable ticket can be fully refunded if the airline makes significant changes in the flight schedule, the flight has a significant delay or the flight is cancelled altogether. 
• Some airlines, (for example United), will refund tickets or change fees in case of special circumstances, (like: death of an immediate family member, jury duty and certain illnesses), if such an event will prevent you to use your ticket. Of course, they require proper documentation.
• Same-day changes allows you to change your domestic flight on most airlines for a fee that is usually lower than regular flight changes fees (or for example, at Southwest, flight changes are free). Same-day changes are allowed within 24 hours before your original flight, or in some cases after midnight on the day of your actual trip; and the requested flight must depart within 24 hours from the time the request is made. You still have to pay any fare difference.
•  Award miles tickets have a different set of rules, specific to each airline.
• Note: the following information related to cancellations and changes fees might not be up to date. Even though we try our best to keep information current it is best for you to check with the airline for their latest updates.

Ticket Changes and Cancellation Fees

Alaska Airlines:

• Same-day changes fee: $25/ticket.
• Free changes for flights within Alaska State.
• Free changes/cancellation made at least 60 days prior to original departure.
• Changes/cancellation made less than 60 days prior to original departure, $125/ticket.

American Airlines:  

• Same-say changes fee $75/ticket for domestic flights, Puerto Rico, U.S. Virgin Islands, Canada, and the Caribbean.
• Same-say changes fee $150/ticket for flights between and connecting through New York JFK and London Heathrow.
• Award miles tickets, at American Airlines, have no charge for date/flight changes made more than 21 days prior to original departure date, (when you don't change your destination).
• Award miles tickets, date/flight changes made less than 21 days prior to the original departure time will have a fee of $75/ticket.
• Award miles tickets destination changes, have a $150fee/ticket.
• Award miles tickets cancellations and miles reinstatement, have a $150fee/ticket for the first ticket and $25 per ticket for any additional award tickets reinstated to the same account at the same time.
• On paid tickets, A Airlines has a $200fee/ticket on domestic travel for any changes and up to $750/ticket on international travel.

Delta Airlines:

• Basic-Economy tickets: no flight changes or refunds allowed, except 24-hrs cancellation for flights booked 7 days or more prior to departure.
• Same-day ticket changes fee $75/ticket.
• Flight changes fees for domestic flights, Canada, Puerto Rico, and U.S. Virgin Islands, $200/ticket.
• For other destinations, the flight changes fees between $200/ticket and $500/ticket.
• If the ticket was issued in U.S or Canada by a travel agency or another airline, including SkyTeam and codeshare partners (not issued by Delta directly) a $50/ticket "external ticket" extra charge will be charged in addition to the flight changes fee that applies.

Frontier Airlines:

• Same-day ticket changes fee $99/ticket, plus any difference in airfare.
• On paid Economy class ticket, the flight changes have a $99 fee per ticket, plus any difference in airfare.
• Changes to award tickets made 8 days or more prior to original departure date do not incur a fee.
• Changes to award tickets made within 7 days of original departure date will incur a fee up to $99/ticket.
• Cancellation fee for award ticket $75/ticket.

Hawaiian Airlines:

• Award miles tickets at Hawaiian Airlines have a cancellation/miles reinstatement fee of $150/ticket for flights between U.S. mainland and Hawaii and for international flights, and $30/ticket fee for flights between the Hawaiian Islands.
• Award miles tickets date/flight changes have a fee of $50 fee/ticket for flights between U.S. mainland and Hawaii and for international flights.
• On paid tickets: date/flight or reroute changes have a $200 fee/ticket for flights between U.S. mainland and Hawaii, and a fee between $50 and $300 /ticket for international travel (like Japan, Korea, Australia).
• On paid tickets: date/flight or reroute changes have a $30 fee/ticket for travel between Hawaiian Islands.
• Most paid tickets are nonrefundable. For restricted refundable tickets, the refund fee is $25 for flights between Hawaiian Islands and $100 for flights between U.S. mainland and Hawaii and for international flights.

JetBlue Airlines:

• Same-day changes fee is $75/person.
• For Blue and Blue Plus changes/cancellations made 60 days or more prior to original departure date have a $75/person fee, plus difference in fare.
• For Blue and Blue Plus changes/cancellations made less than 60 days prior to original departure date have a $75/person fee for fares under $100,  $100/person fee for fares between $100 - $149, and $150/person fee for fares $150 or more.  Plus the difference in fare.

Spirit Airlines

• Paid ticket changes/cancellation fee $90/ticket, when done online.
• Paid ticket changes/cancellation fee $100/ticket, when done on the phone or at the airport.
• Award ticket changes/cancellation fee $110/ticket.

Southwest:

• A purchased ticket is non-refundable, but you can cancel it for a flight credit, which will be good for up to one year from the ticket issue date.
• There is no fee for changing a paid ticket; you only pay the fare difference. Keep in mind that the price usually goes up as you approach the flight date.

United Airlines:

• Basic-Economy tickets: no flight changes or refunds allowed, except 24-hrs cancellation for flights booked 7 days or more prior to departure.
• Same-day changes $75/ticket. 
• To learn more about flight changes, visit United Manage Reservation page.
• Award miles tickets, at United, have a change/cancellation fee of $75/ticket if the change is made more than 61 days prior to original flight date, (for general members).
• Award miles tickets changes/cancellation made less than 60 days prior to original departure have a fee of $125/ticket, (for general members).

Air Canada

• For flights to/from U.S. same-day changes fee $100/ticket for flights between Toronto (YYZ) and New York (JFK) and Newark airports. For flights to/from U.S. same-day changes fee $150/ticket for flights between other airports.
• Changes for Economy-Tango and Economy-Flex tickets to/from U.S. fee $200/ticket.
• Same-day changes for flights within Canada fee $100/ticket, on Rapidair routes and flights between Calgary, Edmonton and Vancouver. Same-day changes for flights within Canada on other routes $150/ticket fee.
• Changes fee for Economy-Tango and Economy-Flex tickets on flights within Canada $100/ticket.
• For international flights same-day changes $100/ticket fee for Economy-Tango and Economy-Flex.