Deciphering 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.

In today’s installment, I’m mostly just explaining a few key terms that you may run across when reading fare rules. Later this weekend I’ll provide some examples of actual fare rules to show how you can put this lesson into practice.

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.


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 into a place like Washington, DC, and the fare only permits Baltimore or Dulles, not the convenient Reagan 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 enbark 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. You fly from AAA to BBB 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 and plane 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.

Open Jaw

Open jaw trips are like a roundtrip but only involve a single shared airport. These may look like AAA-BBB-CCC or AAA-BBB//CCC-AAA. 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-LAX//SNA-SJC, and these generally require combining two one-way fares.

Circle Trip

Like it says, you travel in a circle/triangle/other polygonal approximation. The itinerary will look something like AAA-BBB-CCC-AAA. 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 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


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 few days 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. For example, you may have a roundtrip fare for SEA-FRA-SEA and want to add a one-way fare for SFO-LAX or SEA-LAX to the end to purchase both fares in one transaction. This kind of construction is a requirement for most fuel dumping.

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. It 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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  • paul


    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. For example, you may have a roundtrip fare for SEA-FRA-SEA and want to add a one-way fare for SFO-LAX or SEA-LAX to the end to purchase both fares in one transaction. This kind of construction is a requirement for most fuel dumping.”

    Are you sure about that? I thought that an add-on was an additional fare to get to the hub city, so XXX-SEA or SEA-YYY in this case.

    Here’s a page that explains it:

    • Scottrick

      You may be right. I’ll be honest that the term “add-on fare” usually confuses me, and I’ve given the best explanation as I have it in my mind. Clearly it is not the same as an end-on-end or back-to-back fare.

      However, sometimes I think the fare rules are tailored toward the kind of trips people want to take. A normal person would want to fly SEA-LAX at the end of SEA-FRA-SEA. Few would want to fly LHR-CDG at the end of SEA-FRA-SEA, so why mention if that’s allowed (and no, that doesn’t mean LHR-CDG is a working 3X)? I have had more luck when pairing a 3X if the fare rules indicate that add-ons are permitted, so I assume there is a link. This doesn’t necessarily mean it’s treating the 3X as an add-on. It could just mean that the fare is more open to combinations, including add-ons and also my 3X.

      • paul

        I just looked to find a fare that had “Add-ons NOT permitted” in the rules, but with with other combinations permitted with 2 carriers. I added on a random unrelated one-way fare onto the ticket using one of those carriers. I’m pretty certain the add-on rule is not related to the 3x, but is either allowed by the end-on-end or circle-trip rules.

  • paul

    I just did a bit of research into this after finding this comment:
    “Add-on fares can never be displayed or priced alone”

    So, an example of what I believe an add-on is, is this:
    Go to ITA and in departing from, use Nearby, and 300 miles from FRA
    Routing code: / f ..EHNCDE5
    Dates 18 March – 25 March
    Routing code: /f ..WHRCDE5

    The base flight that you’ll find is the 979 euro flight from FRA-BKK
    You’ll see other flights via FRA that cost a little bit more, but do not have a separate fare component. These additional costs are the “add-ons” I believe.


    @4e0365549269325174baada531914c40:disqus , I’ve used your post to decipher some fare rules and really appreciate the effort and clarity of your explanations. One thing I cam accross that I am not sure about though is that it says “SIDE TRIPS ARE PERMITTED.” Maybe I’m just being dump, but do you know what that means?

    • Scottrick

      A side trip involves traveling from A to B and back to A. So for example, a side trip to Frankfurt on your way to Nice would look like IAD-CDG-FRA-CDG-NCE.