How is fare difference calculated during a flight change?

The fare difference during a flight change is calculated by comparing the price of the original ticket with the fare for the new travel date, time, route, or cabin. If the new flight costs more, the passenger pays the additional fare difference. Airlines may also add a change fee, reissue fee, service charge, and any increase in taxes or airport fees. If the new flight is cheaper, the remaining amount may be refunded, stored as travel credit, or forfeited, depending on the airline’s fare rules. The calculation also considers ticket class, seat availability, route restrictions, advance purchase requirements, and promotional fare conditions. For multi-city or connecting itineraries, the airline may recalculate the entire journey rather than one segment. A Flight API checks availability and fare rules in real time, then displays the amount payable before confirmation. This ensures transparent pricing and helps travelers understand costs involved in changing a flight booking.