The minimum age for an infant to fly varies by airline, but most carriers require a baby to be at least 7 days old before they are permitted to board a commercial flight. Some airlines, such as IndiGo, allow travel for infants as young as 3 days old, while others may have stricter policies. In special medical cases, an infant under 7 days may be allowed to fly, provided a physician issues a medical clearance certificate. In 2026, it is standard for airlines to require proof of age at check-in, such as a birth certificate, hospital discharge summary, or passport. Parents should also be aware that the pressurized cabin environment and recycled air can be difficult for newborns, so consulting a pediatrician before a trip is highly recommended. Regardless of age, infants under two years typically travel as "lap children" on domestic flights, though they must still be included in the reservation and often incur a small fee or tax.