An Introductory Guide to Fare Rules

I’m discussing airline inventory this week, including fare class availability, fares themselves, and fare construction. A lot of talk about fares for a product some people don’t think is priced very fairly at all. But maybe that’s just because they don’t know what to look for. I get upset, too, when things seem unnecessarily opaque. I’ll try to clear things up.

In today’s installment, I’m mostly just explaining a few key terms that you may run across when reading fare rules.

Permitted Routing

This is the route you are allowed to travel with this fare. There may be several different options available. For example, the permitted routing could look like SEA-SFO/OAK/SJC-JFK/EWR-LHR. In routing language, dashes indicate flights between airports, and slashes indicate an option between two or more airports. This example means you will fly from Seattle to either San Francisco, San Jose, or Oakland, then to either JFK or Newark (not La Guardia), and then to London Heathrow (not Gatwick or Luton).

I will use two slashes instead of one to indicate that there is a break in the itinerary rather than an option between two airports. For example, SEA-SFO//SJC-SEA means you fly from Seattle to San Francisco and later from San Jose to Seattle, making your way from San Francisco to San Jose by some other means as part of an open jaw. Thus, with two slashes you actually fly through both airports, whereas with one slash you have a choice between them.


These are equivalent airports as far as the fare rules are concerned. Frequently you will see something like SFO/SJC/OAK in the fare rules. It doesn’t necessarily mean the airline has flights between all of the city pairs listed in its routing rules (maybe you can only get to one by connecting elsewhere), or even that it operates any flights at all to some of those airports. Co-terminals often make a lot of sense due to geographic proximity.

On the other hand, sometimes certain nearby airports WILL NOT be listed as co-terminals, which is annoying when you want to fly to a place like Washington, DC, and the fare only permits Baltimore or Dulles, not the convenient Reagan National airport.

Maximum Permitted Mileage

Rather than specify a particular routing, international fares often specify a maximum permitted mileage. Say you want to fly from San Francisco to London. The MPM may be something like 14,000. There may be a few other rules like the maximum number of transfers/connections and which regions they can be in, but otherwise the only requirement is that you keep the total distance flown under 14,000 miles.

Unless you’re trying to force a crazy routing or having difficulty finding fare class availability, I wouldn’t worry about MPM. This is information you can look up with a service like KVS Tool and is not airline specific. However, some airlines will have a policy that permits you to go over by a certain amount, like 10 or 15%, on award trips. On revenue trips, there may be a fare surcharge that matches the excess mileage.


These are the individual flights where you embark and debark an aircraft. Again, simple enough, but most people in my experience use the word “flight” instead of “segment.”

Nonstop Flight

Truly what it sounds like. For example, you fly from SEA to LHR without stopping.

Direct Flight

A deceptive ploy by the airlines for the most part. A direct flight refers not to the actual path the airplane travels but rather whether the assigned flight number changes en route. For example, flight 123 may travel from SEA to LAX to JFK to LHR with gate, plane, and crew changes at each airport. If you don’t pay close attention, you might book flight 123 hoping for a nonstop trip from SEA to LHR and not realize you have to change planes in LAX and JFK.

Not only that, but the fact these four separate trips all share the same flight number doesn’t guarantee the airline will hold one flight if the preceding one is delayed. Don’t think of a direct flight as anything other than a normal connecting flight. In fact, be very concerned. Sometimes the number of miles awarded will be as if it were a nonstop flight even though you spent a lot more time in a seat. Check the rules of your loyalty program.

Open Jaw

Open jaw trips are like a roundtrip but only involve a single shared airport. These may look like SFO-EWR-SJC (the jaw is open at the origin on the West Coast) or SFO-EWR//JFK-SFO (the jaw is open at the destination on the East Coast). Generally the open part of a jaw must be a shorter distance than either of the two flown segments. A double open jaw is one where both ends are open, such as SFO-EWR//JFK-SJC, and these generally require combining two one-way fares.

Open jaws can be a great way to save some money. A lot of fares these days don’t discriminate between booking a round trip or two one ways. If you have lots of airports to choose from, you’ll have more flexibility to find a cheap one way fare there and a cheap one way fare back. Also, if you’re doing something like a European tour you won’t have to double back to where you first arrived.

Circle Trip

Like it says, you travel in a circle/triangle/other polygonal approximation. The itinerary will look something like SFO-ORD-DFW-SFO. Alternatively, a circle trip may mean a round trip but one that uses a different one-way fare basis codes in each direction. A true round trip would use a single fare basis code.


These are airports where you stop along the way. Simple enough, but sometimes the word “transfer” doesn’t always make sense to people who think of these as “connections.”

In general, you are permitted 4 hours to make a domestic connection and 24 hours to make an international connection. If there are very infrequent flights, like two flights a day 12 hours apart, you’ll be allowed to stay longer than 4 hours but only if you take the first connection available.

If you arrive after the last connecting flight of the day, you will be granted additional time until the next connecting flight the following morning (or another day if there aren’t daily flights).This can be a great way to take advantage of opportunities for mini-trips if you aren’t permitted a stopover, which is a real break in your trip to spend a few days and pick up later. Getting 24 hours to run into a favorite city for a nice meal can be better than not seeing it at all.


A stopover is a break in your itinerary to spend time in a connecting city. You may be traveling from New York to Dubai via London. Rather than spend three hours connecting in London, you can elect to stay there for a week and have a mini trip-within-a-trip. Sometimes this is free (especially on some award trips) and sometimes it costs $100 or so.


Any time you are trying to combine two fares you will have to worry about combinability. Note that there ARE single fares that permit some crazy routings but get you back to the same place, like round-the-world fares. However, you can generally assume that anything other than a simple roundtrip or one-way ticket is going to require combining two fares. Usually most search engines will tell you when this is the case.

Examples of combinations include circle trips, open jaws (sharing only the origin or destination airport, not both), and end-on-end combinations (a combination of two roundtrip fares).

Because there are multiple fares are involved but purchased as one transaction, you might wonder which set of fare rules apply. It is very difficult to figure out how these rules work together, and it isn’t always easy to predict whether two fares will combine properly. However, you can generally assume that the most restrictive set of rules will apply. So if you are combining a non-refundable G fare with a refundable Y fare, then typically both fares will be non-refundable.


You will usually see this written as “add-ons permitted” or “no add-ons permitted.” An add-on is an extra flight added on to the beginning or end of an itinerary, usually for reasons like getting you to an international gateway. For example, you may have a roundtrip fare for SFO-CDG-SFO and want to add a one-way fare for SEA-SFO or SFO-SEA because there aren’t any nonstop flights from Seattle to Paris. Add-on fares cannot be sold by themselves but rather only in combination with another fare.

To be honest I am not especially clear on how this rule works, but you can read more about it from sources like this one.

Back-to-Back Ticketing

This is a practice forbidden by all airlines to my knowledge. It involves purchasing two separate tickets and using them out of order or using only parts of each ticket.

In the first example, using them out of order, you may buy two roundtrip tickets from Seattle to London but stagger the dates like so:

  • SEA-LHR on the 1st (ticket A)
  • LHR-SEA on the 3rd (ticket B)
  • SEA-LHR on the 10th (ticket B)
  • LHR-SEA on the 12th (ticket A)

Why is this forbidden? Perhaps there is a minimum stay requirement of seven days. Ticket A and ticket B both meet these requirements, qualifying for a cheaper fare. But the passenger is actually traveling on two separate roundtrips with only two days in London each time. He or she is circumventing the fare rules to pay less than required.

In the second example, intentionally using only part of each ticket, you may book the same tickets as above but only use the first leg of each. Maybe you don’t actually need to go to London twice, but it’s still cheaper to buy two tickets and throw away half of each rather than pay full price for a ticket that lets you stay less than seven days.

End-on-End Ticketing

End-on-end ticketing is when you place fare B within fare A. It is very similar to the first example of back-to-back ticketing. However, the fare rules will tell you if end-on-end ticketing is permitted, and there isn’t any particular reason why this wouldn’t be okay because it’s perfectly understandable that there won’t always be a single fare for every trip between two cities. Your purchase will look something like this:

  • SEA-EWR (fare A)
  • EWR-BOS (fare B)
  • BOS-EWR (fare B)
  • EWR-SEA (fare A)

United doesn’t fly directly to Boston from Seattle, but it does fly directly to each city from Newark. Perhaps the fares for each of those roundtrips together is cheaper than a single fare for Seattle to Boston that permits a connection. So you would buy fare A to get you between Seattle and Newark, and fare B to get you between Newark and Boston. However, they are all on the same ticket, not like what you saw above in back-to-back ticketing where they were purchased separately.

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Scott created Travel Codex after learning how to travel better on a budget during grad school. He now flies over 150,000 miles every year.
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  • vortix

    GREAT article…thanks for the info!

  • Travel Summary

    I love your articles. So informational to the less-savvy traveler!

  • rick b

    you SHOULD worry about MPM because those come in very handy when tacking on one-ways or stop-overs on AA or UA awards. Sometimes MPMs are very generous and allow routing through a city or region that’s completely out of the way.

    • Scottrick

      True. MPM matters more for any unusual routings.

      • rick b

        Btw, your comment about open jaw maximum distance isn’t quite right. For example, EWR – PTY (destination) – IAH (stopver) – NRT is bookable with 50k miles in coach on UA.

        • Scottrick

          But wouldn’t you agree that this is an exception, a glitch that isn’t intentional? It’s kind of hard to argue that the rules are different when the award you use as evidence is already mis-priced.

          • rick b

            that’s not mis-priced, it’s a perfectly legal award where you add the mileage for US-Caribbean to Caribbean-Japan. You can do US – Europe – US (stop) – South America as well. It’s well within UA’s rules for 2 open jaws and 1 stopover.

          • Scottrick

            Fair enough. I was thinking of the price of a US-Japan RT. I think my original statement was correct, though, that “generally” an open jaw requires the open portion to be shorter than either of the of the flown portions.

  • DL

    Nice job. Just want to point out that your open jaw example “SFO-EWR//JFK-SFO” could actually be a round trip if the fare allows co-terminals. EWR and JFK and LGA are usually co-terminals. And co-terminals do not count as an open jaw if your fare allows one open jaw. So if a passenger is looking for more flexibility, they could take advantage of an open jaw at the other end: SFO-EWR//JFK-SEA.

    • Scottrick

      Good point. I don’t think I’ve ever taken a trip with such a small jaw. Usually I’ll do something like fly into LHR and fly out of ZRH. (This particular example is a great way to avoid the UK passenger duty, which is only levied on departures, not arrivals.)