It varies. They will often wait a little while, especially if it's the last flight of the day and even moreso if there are multiple passengers making the same connection. I've had Delta wait for me after inbound connection delays on several occasions.

Generally, airlines do not wait for individual late passengers, but there are notable exceptions in 2026. An airline is most likely to hold a flight if a large group of passengers (e.g., 20+) is delayed on a single incoming flight, as rebooking dozens of people is more expensive than a 15-minute departure delay. Flights might also wait if it is the last service of the day to a specific destination, or if the delay won't cause the flight crew to exceed their legal "duty hours." Decisions are made by "Operations Control Centers" using real-time data to balance the cost of the delay against the cost of hotel vouchers and rebooking fees. If you are on a "protected" connection (booked on one ticket), the airline is legally responsible for getting you to your destination, so while they may not hold the plane for you, they must provide a seat on the next available flight, along with meals and overnight accommodation if necessary. In high-traffic hubs, however, strict "slot" times usually mean the plane must push back on schedule regardless of who is missing.