While each airport will have its own procedures, security generally opens two to three hours before the first departure of the day, and remains open until the last passenger has gone through.

In 2026, how early you can pass through airport security depends on whether you have checked bags and the specific rules of the airport or airline. If you are traveling with only a carry-on and have a mobile boarding pass, you can typically go through security as soon as the checkpoints open for the day (often 4:00 AM or earlier). Most airports will allow you through as long as your flight is scheduled for the same calendar day. However, if you need to check a bag, you are usually limited by the airline's counter hours, which typically open 3 to 4 hours before your scheduled departure. At major hubs like London Heathrow or JFK, security may restrict entry to 4–6 hours before a flight to prevent terminal overcrowding. For those with Lounge Access, arriving early is a popular strategy, but be aware that if your flight is very early the next morning (e.g., a 1:00 AM flight), you might not be allowed through until after midnight. Always check the "Check-In" window in your airline's app, as this is the primary gatekeeper for your ability to enter the secure side of the terminal.