For international flights: If you are traveling internationally, attempting to board your flight with an expired passport will not be possible. Even if you are permitted on the plane, you will likely be turned away upon arrival. It is not worth the risk, so renew your passport before you travel.

Attempting to travel with an expired passport generally results in being denied boarding at the airport. Airlines are legally required to verify that passengers have valid travel documents for their destination; if they allow you to fly with an expired passport, the airline can be heavily fined, and you will be deported immediately upon arrival. Even if you are a citizen of the country you are flying to, most airlines will not let you board an international flight without a valid document. If you find yourself at the airport with an expired passport, you must look for an "Urgent Travel" or "Emergency Passport" service at a nearby passport agency or consulate. Some countries allow their citizens to return home on an expired passport via land borders, but for air travel, it is virtually impossible. Additionally, many countries require your passport to be valid for 3 to 6 months beyond your date of departure, so even if it isn't "expired" yet, you could still be denied entry if you are too close to the expiration date.