Everything You Need to Know About Booking Mistake Fares

Sometimes, a flight deal seems too good to be true. Maybe you've spotted a $300 ticket to Japan, or a flight to Australia for under $500 — numbers far below the typical price point. When airfare drops this low, it's often labeled as a mistake fare, an error fare, or sometimes a "fat finger" fare. These names indicate what happens when a misplaced decimal point, miscalculated currency conversion, or data entry error accidentally publishes incorrect (and incredibly cheap) ticket prices.

Sometimes, mistake fares are the result of a ticket posted before airport taxes or fuel surcharges are added. Other times, they're simply caused by a computer glitch. Whatever the cause, mistake fares can result in truly outrageous flight prices, the likes of which wouldn't happen during even the best airfare sale.

Related: More flight deals

Where to Find Mistake Fares

Any site or app specializing in flight deals (Scott's Cheap Flights is perhaps the most popular site, but you can also find these deals on Airfare Spot and The Flight Deal) will spot mistake fares before the airline even notices that their $4,000 business class seat is selling for $400.

The Downside of Error Fares

In the past, airlines were required by the Department of Transportation to honor mistake fares, however under-priced they were. The landmark United Denmark fares, however, set in motion the DOT's decision to allow airlines to withdraw these tickets. In February 2015, $51 first class flights from New York to Copenhagen were found on United's Denmark website — but they could only be booked in Danish krone when travelers indicated Denmark in their billing address (even though most purchases weren't made from Denmark-based individuals).

The DOT determined that there was "evidence of bad faith," and that travelers had to intentionally "manipulate the search process…to force the conversion error." In situations such as this, booking mistake fares is largely frowned upon — not only by airlines and government organizations but also by people who, typically, book full-fare tickets.

Of course, you can still find and book mistake fares from airlines' American websites — but there is a small chance your ticket will be canceled.

How to Book Mistake Fares

Error fares can typically be booked through an airline's website or an OTA (an online travel agency). Scott's Cheap Flights recommends that when travelers suspect a deal is a mistake fare, they book directly through the airline whenever possible — and quickly, before the carrier figures out what's up. If you book directly with the airline, you get a 24-hour grace period after booking so you can cancel and get a full refund if you have second thoughts.

Months after the Danish United fares were published — and retracted — the DOT ruled that, if an airline could prove fares were truly published by accident, they could rescind those tickets."The burden rests with the airline…to prove to the Enforcement Office that an advertised fare and the resulting ticket sales constitutes a mistaken fare situation," the government department stated.

Nonetheless, it's still strongly recommended that travelers who think they're booking a fare published in error wait until the flight has been ticketed to make additional travel plans. Scott's Cheap Flights says that about 80 to 90 percent of the mistake fares they've seen are honored, but that leaves 10 to 20 percent that are canceled. If your ticket is canceled, you will be refunded, so it's best to wait a couple of weeks to make any non-refundable plans. According to Scott's Cheap Flights, most airlines will notify you within 72 hours if the mistake fare will not be honored.