In 2026, the general rule of thumb is 2 hours for domestic flights and 3 hours for international flights, but several factors can shift this recommendation. If you are traveling during peak holiday periods, have checked luggage, or are departing from a "mega-hub" like Atlanta (ATL) or London Heathrow (LHR), the full 3-hour window is essential to navigate TSA/security lines and the often-lengthy walk to distant gates. Conversely, if you have TSA PreCheck or CLEAR, are traveling with carry-on only, and have checked in digitally, you can often arrive 90 minutes before a domestic departure without stress. For international travel, the 3-hour window accounts for document verification (passports/ETIAS) and the fact that boarding typically begins 45 to 60 minutes before the scheduled take-off. With the 2026 integration of more biometric gates, the "bottleneck" has moved from check-in to security, making your specific airport’s current "wait time" (usually found on their app) the most accurate gauge for when to leave.