Who this is for: anyone who has seen a transatlantic fare priced like a domestic one and wants to know whether to book it, and what happens if they do.
How we know: Sources are listed at the end. The regulatory history is from the text of the rule and a law-firm summary of the DOT's 2015 policy statement; the DOT's own pages were inaccessible to our loader on the date above, so we cite the summary and say so. Past examples come from reporting by The Points Guy. Nothing here is a Wildly measurement.
Mistake fares explained in one paragraph: an airline or agency publishes a price that is far below what it intended, usually through a filing error, a currency mistake or a fuel-surcharge omission; people book it; and then one of two things happens. Either the airline honours it, or it cancels the tickets and, under a US Department of Transportation policy in force since 2015, refunds the fare and any reasonable out-of-pocket costs you incurred relying on it. The rest of this guide is the detail: how the errors happen, exactly what the DOT policy says, what to expect in the days after booking, and how alerts catch these fares.
How an error fare happens
Fares are filed centrally and distributed to every seller. ATPCO "engages in the collection and distribution of fare and fare-related data for the airline and travel industry", handling "over 446 million active fares" and "an average of 18 million fare changes each day" (Wikipedia: ATPCO). Every fare carries a fare basis code and rules, and its first letter maps to a booking class that controls how many seats sell at that level (Wikipedia: Fare basis code). With that volume, the failure modes are predictable:
- A missing surcharge. Long-haul fares are often a small base fare plus a large carrier-imposed surcharge. Drop the surcharge and a $1,200 ticket prices at $300.
- A currency or decimal error. The case that triggered the current US policy was United in February 2015, when fares filed in Danish kroner priced first-class transatlantic tickets at a tiny fraction of their value; The Points Guy's guide references that case as the prompt for the DOT's statement (The Points Guy).
- A wrong booking class or routing. A premium fare filed against an economy class, or a fare that was meant for one market published to another.
Because the fare is distributed everywhere at once, it appears on Google Flights, the airline's site and every agency simultaneously, and it usually lasts from an hour to a day before someone notices.
What the DOT requires
The underlying rule is 14 CFR 399.88, which makes it "an unfair and deceptive practice" for a seller of air transportation to increase the price after purchase, with the sole exception of a government-imposed tax or fee increase agreed to in writing (14 CFR 399.88). Read literally, that rule meant that once you bought a mistake fare, the airline had to fly you. Cozen O'Connor's summary confirms that DOT had "generally required airlines and sellers of air transportation to honor such fares once a consumer purchased the fare and received confirmation of the purchase" (Cozen O'Connor).
On 8 May 2015, DOT's Office of Aviation Enforcement and Proceedings issued a policy statement changing that. As summarised by Cozen O'Connor, the Enforcement Office will not pursue an airline that cancels a mistaken fare provided the airline does two things: (1) "demonstrate that a fare was a mistaken fare", and (2) "make consumers 'whole' by reimbursing them for any 'reasonable, actual, and verifiable out-of-pocket expenses'" in addition to refunding the ticket. Reimbursable expenses include "non-refundable hotel reservations, destination tour packages or activities, cancellation fees for non-refundable connecting air travel and visa or other international travel fees". The burden of proof "rests with the airline or seller of air transportation". The policy was described as "temporary" and effective "until DOT issues a final rule that specifically addresses mistaken fares" (Cozen O'Connor).
Two points people miss. First, the policy statement does not define a mistaken fare; The Points Guy notes that "the current DOT Mistaken Fare Policy Statement doesn't provide any definition for mistake fares" and that airlines decide case by case (The Points Guy). Second, the reimbursement obligation is real: if you booked a non-refundable hotel in reliance on the ticket and the airline cancels, you can claim that cost. Keep receipts.
We could not load DOT's own pages for the 2015 statement or the 2015 United decision on the date above (the department's site returned access errors), and we did not find a later final rule in the sources we loaded. The Points Guy's 2018 guide treated the 2015 statement as still operative. Treat the position as: the 2015 policy is the operative guidance as far as the sources we could load show.
What happens after you book
From The Points Guy's guide, which is the most detailed account we could load (The Points Guy):
- Timing. Airlines "may cancel mistake fares at any point"; there is no defined window. In one Delta case, cancellations "rolled in slowly across about 24 hours".
- What gets honoured. The author's rule of thumb is that fares priced "more than 30-40% of what is common for that airline on that route" typically are not cancelled; deeper errors more often are. That is an observation from experience, not a rule.
- Refund timing. Airlines must refund within seven days of receiving a complete refund request.
- Advice. "Keep your expectations tempered", and do not book non-refundable hotels, tours or connecting flights until the airline has confirmed the ticket, or at least not before the fare has been widely reported and the airline has had time to react.
A sensible personal policy: book the fare if you would be genuinely happy to take the trip, pay with a card that makes refunds easy, do not buy anything non-refundable for at least a week, and treat a confirmation email as a maybe until the ticket has been issued and a few days have passed.
How alerts catch mistake fares
Error fares are short-lived and land on Google Flights at the same moment they land everywhere else, which makes them a good fit for threshold alerts and a poor fit for prediction tools.
- A Wildly alert checks the route you name on Google Flights once a day and emails you when the lowest fare is at or below your target. Set the target well below the route's typical band and the alert will fire on the kind of drop an error produces. A daily check will miss a fare that lives for an hour and catch one that lives for a day, which is roughly the split. Plus or minus 3 days of flexibility widens the net, because error fares are usually filed for a range of dates. The free plan covers this; details on /pricing.
- Route pages give you the reference point. New York to Paris, Los Angeles to Tokyo, Chicago to London and Newark to Lisbon each show the lowest fare in the latest daily check with its date and, once enough days accumulate, typical, good and great bands. A fare far below the "great" band on a route with a long history is either a sale or an error; either way, act on it. How the checks are made is on /methodology. Wildly records daily prices on about 240 routes; route pages show observed ranges as they accumulate.
- Google Flights tracking is a useful second channel because Google emails when a tracked price changes significantly, though the check schedule is not published; see Google Flights price tracking explained. For how the other alert services compare on speed, see flight price alerts compared.
FAQ
Are airlines required to honour mistake fares? Not since May 2015. Under DOT's enforcement policy, an airline may cancel a fare it can show was a mistake, provided it refunds the ticket and reimburses reasonable, actual and verifiable out-of-pocket expenses you incurred in reliance on it.
How long after booking can the airline cancel? There is no defined window in the policy. Cancellations in past cases have arrived within hours to a few days.
Can I claim my non-refundable hotel if the airline cancels? Under the 2015 policy, yes: non-refundable hotel reservations are listed among the reimbursable expenses. You need documentation.
Is a very low fare always a mistake? No. Sales, new-route launches and off-season pricing produce low fares legitimately. A fare that is low but within the range of the route's history is probably a sale; one that is a fraction of the route's "great" band is more likely an error.
Do price alerts catch mistake fares? Threshold alerts do, if the fare lasts long enough to be checked. A daily check catches fares that live for a day; nothing catches every one-hour glitch.
Sources
- Cozen O'Connor: DOT Revises Its Mistaken Fares Enforcement Policy: https://www.cozen.com/news-resources/publications/2015/dot-revises-its-mistaken-fares-enforcement-policy
- The Points Guy: The Comprehensive Guide to Canceled Mistake Fares: https://thepointsguy.com/airline/the-comprehensive-guide-to-canceled-mistake-fares/
- 14 CFR 399.88, Prohibition on post-purchase price increase (Cornell LII): https://www.law.cornell.edu/cfr/text/14/399.88
- Wikipedia: ATPCO (Airline Tariff Publishing Company): https://en.wikipedia.org/wiki/ATPCO
- Wikipedia: Fare basis code: https://en.wikipedia.org/wiki/Fare_basis_code