In 2026, United Airlines' policy on carry-on bags depends entirely on your fare class. If you book a "Basic Economy" ticket on a domestic or short-haul international flight, you are not allowed a full-sized carry-on bag; you are restricted to one small personal item that fits under the seat in front of you. If you bring a carry-on bag to the gate with a Basic Economy ticket, you will be required to check it and pay the standard checked bag fee plus a $25 to $65 gate handling charge. However, if you book a standard "United Economy" fare or higher, a full-sized carry-on bag is included for free. Furthermore, MileagePlus Premier members and primary cardholders of qualifying United co-branded credit cards receive a "carry-on allowance" even when flying in Basic Economy. For long-haul international flights (transatlantic/transpacific), United typically allows one free carry-on regardless of the fare class, but it is essential to check your specific flight details in 2026, as baggage rules continue to be a primary way airlines "unbundle" costs.