Methodology

Distance

Distance between airports is the great-circle distance computed with the Haversine formula on a sphere of radius 6,371 km, using each airport's latitude and longitude. This is the shortest path over the earth's surface. Real flight paths are longer because of airway structure, restricted airspace, and wind routing — typically by 2–6% on long-haul sectors.

Flight duration

Duration is estimated from the great-circle distance and a typical jet cruise profile, plus a fixed allowance for taxi, climb, and descent. It is an aircraft-agnostic estimate, not a schedule lookup: it does not know your airline, aircraft type, routing, or the jet stream on the day. Eastbound transatlantic and transpacific flights are usually faster than our estimate, westbound slower, because of prevailing winds.

Time zones

Each airport carries an IANA time zone identifier (for example Europe/Stockholm). Offsets are resolved at runtime through the browser's Intl.DateTimeFormat API rather than hard-coded, so daylight saving transitions, half-hour and 45-minute offsets, and rule changes are handled by the platform's up-to-date tz database.

Jet lag severity and recovery

Severity is derived from the number of time zones crossed and the direction of travel. Crossing fewer than three zones is treated as mild, three to six as moderate, and more than six as severe. Recovery is estimated at approximately one day per zone for westward travel and up to 1.5 days per zone for eastward travel, reflecting the free-running human circadian period of slightly over 24 hours, which makes phase delays (west) easier than phase advances (east).

The day-by-day plan places light exposure relative to your estimated circadian minimum, roughly two hours before habitual wake time. Light before that point delays your clock; light after it advances your clock. Eastward plans therefore front-load morning light and block evening light, and westward plans do the reverse.

This output is an educational estimate, not medical advice. It does not account for shift work, sleep disorders, medication, or individual chronotype.

Corrections

If you find an airport with the wrong coordinates or time zone, or a calculation that looks off, we want to know. More context on the project is on the about page.