Status: checked against official sources; automated independent review
FREQUENT FLYER GLOSSARY
What is baggage interlining?
Baggage interlining is the arrangement that lets one airline take your checked bag and hand it to another carrier so you do not collect and re-check it at the connecting airport. Whether a bag is through-checked depends on the airlines involved, the ticket, the airports and the itinerary, and Delta Air Lines treats a single ticket and two separate tickets as distinct cases. [2]
Facts checked: 18 October 2026
Key takeaways
- Interlining is about the bag rather than the passenger: a carrier that interlines can tag a checked bag past the connection so it reaches the ticketed final destination without being reclaimed in between.
- American Airlines requires checked bags to travel to the same ticketed final destination as the passenger, and bags can only be checked on the day of travel. [1]
- American says you may have to pay bag fees again if you connect on another airline, or if your connection on American is more than 16.5 hours later. [1]
- Arriving in the United States from an international city on American, you claim your checked bags before going through Customs. [1]
How does baggage interlining work?
Two things have to line up. The first is a commercial arrangement — an interline agreement — that allows one airline to accept another carrier's ticket and carry a bag beyond the end of its own flight. The second is a continuous journey recorded on one ticket, because that is what gives the check-in agent a final destination to print on the bag tag. When both are present, the bag is usually through-checked, as described in the guide to through-checked baggage: tagged once at the first counter and routed to the last airport on the itinerary.
Delta Air Lines presents the subject as through-checked baggage and splits its guidance into a single ticket and two separate tickets with multiple airline carriers. [2] The split matters because a single ticket gives the bag one final destination, while two tickets create two contracts of carriage and a handover point between carriers.
American Airlines expresses the same idea as a condition of acceptance: bags can only be checked on the day of travel, and they must travel to the same ticketed final destination as the passenger. [1] Where the flight is a codeshare operated by a partner, American directs passengers to the operating airline for details. [1]
What changes when the journey is on separate tickets?
Separate tickets mean separate contracts, and each one covers only the carriage it was sold for. That does not mean the bag must be reclaimed, but it does move the question to the second carrier and to the ground arrangements at the connecting airport — the situation the separate ticket connection checklist is built around.
American's conditions of carriage show the practical cost of a split. The airline warns that passengers may have to pay bag fees again when they are connecting on another airline. [1] A second set of fees can also appear when the connection on American itself runs longer than 16.5 hours, even without any change of carrier. [1] Budgeting for a checked baggage allowance on a two-ticket journey therefore means budgeting for two sets of rules.
The same document separates the carriers' roles when something goes wrong: if you arrive at your final destination on another airline, American asks you to check with that airline for information about delayed bags. [1]
Where do you still collect your bags?
Through-checking is not the same as never touching the bag again, because border control overrides it. American says that when you arrive in the United States from an international city, you claim your checked bags before going through Customs. [1]
Length of connection and any change of airline are the other points where a bag stops travelling on one tag. American's fee language singles out two situations — a connection on another airline, and a connection on American of more than 16.5 hours — in which a passenger may pay bag fees again. [1] If the plan goes wrong at that point, the missed connection action plan covers what to do first.
Exceptions and limits
- Liability caps. For checked bags lost, damaged or delayed on domestic American flights, American pays the provable value of the losses up to US$4,700, or up to US$5,000 where the passenger declares excess value. [1] On international journeys, the Warsaw Convention and the Montreal Convention set the liability rules. [1]
- One claim only. American may reject a claim where the passenger submits the same claim with more than one airline. [1] On a two-carrier journey that turns the choice of which airline to file with into a decision rather than a duplication — see the delayed or damaged baggage claim checklist.
- Allowances tied to a status account. United's MileagePlus rules require members who receive benefits such as an additional baggage allowance to keep their MileagePlus number on the entire reservation, and on any reservation created from the original one, throughout the travel concerned. [6] Where a companion's benefit comes from the member's status and the member stops travelling on the original reservation, the companion loses that benefit. [6]
- Airline-by-airline rules. Each carrier's conditions govern its own segment, so a through-tag does not carry one airline's fee waivers, allowances or claim time limits onto another carrier's flight. [1]
Frequently asked questions
Are checked bags transferred to another airline automatically?
Only where the carriers' arrangements and the ticket allow it. American accepts bags only to the same ticketed final destination as the passenger, [1] and Delta separates the single-ticket case from the two-separate-ticket case in its through-checked baggage guidance. [2]
Do you pay baggage fees twice on separate tickets?
You may. American says passengers may have to pay bag fees again when connecting on another airline, or when the connection on American is more than 16.5 hours later. [1]
Do you have to collect bags when entering the United States?
On American, yes: when you arrive in the U.S. from an international city you claim your checked bags before going through Customs. [1]
Which airline handles a delayed bag claim after a two-carrier journey?
American directs passengers who arrive at their final destination on another airline to that airline for delayed bag information, and it may reject a claim submitted to more than one airline. [1]
Does a status baggage allowance follow you across an itinerary?
United's MileagePlus rules require the member's number to stay on the entire reservation, including any reservation created from the original, for benefits such as an additional baggage allowance to apply. [6]
Sources
Sources checked on 18 October 2026. The rules described here are American Airlines' conditions of carriage, Delta Air Lines' baggage guidance and United's MileagePlus programme rules; other carriers, including British Airways, Emirates Skywards and Singapore Airlines KrisFlyer, are not covered on this page.
- American Airlines Conditions of Carriage, checked 18 October 2026
- Delta Air Lines baggage policy and fees overview, checked 18 October 2026
- United Airlines MileagePlus programme rules, checked 18 October 2026