Jet lag calculator
How many hours your body clock has to move, how long it will take, and exactly when to sleep and when to seek or avoid daylight.
40.7494°, -73.9819° · America/New York
48.8667°, 2.3333° · Europe/Paris
How the plan is calculated
Your body clock is a roughly 24-hour rhythm in the brain’s suprachiasmatic nucleus, reset mainly by light. Circadian research (for example the phase-response curve work summarised by Eastman and Burgess) shows that light in the few hours after your core body temperature minimum advances the clock, and light in the hours before it delays the clock.
- We compute the time shift between your origin and destination today, including daylight saving time.
- Eastward we assume the clock can advance about 1 hour a day; westward it can delay about 1.5 hours a day.
- Up to three days before departure we shift bedtime by an hour a day in the direction of travel, so you land partly adapted.
- Light windows sit in your waking hours: the first three hours after waking (to advance) or the last three before bed (to delay), matching the direction of the shift.
Planning the flight itself? The flight distance calculator estimates flight time, and sunrise and sunset times tell you when daylight is actually available at your destination.
Frequently asked questions
How long does jet lag last?
A common rule of thumb is about one day per time zone crossed eastward and a bit less westward, because the body clock shifts later (about 1–1.5 hours a day) more easily than earlier (about 1 hour a day). Timed light exposure and gradually shifting sleep before you fly can cut that noticeably.
Why is flying east worse than flying west?
Most people’s internal clock runs slightly longer than 24 hours, so it naturally drifts later. Flying west asks it to go later, which is easy; flying east asks it to go earlier, which fights its natural tendency.
How does light help with jet lag?
Light is the strongest signal to your body clock. Light in the hours after your body temperature minimum (usually 2–3 hours before your normal wake time) shifts the clock earlier; light in the hours before it shifts the clock later. Getting the timing wrong can push you the wrong way, which is why the plan tells you when to seek and avoid light.
Should I take melatonin?
Melatonin can help some travellers shift faster, but dosing and timing matter and it is regulated differently by country. Ask a pharmacist or doctor; CoordKit does not give medical or dosage advice.
What does the AI coach do?
It turns the calculated schedule and your own situation (for example an early meeting on day one, or travelling with children) into a short, practical plan in plain English. It only runs when you press the button, and the calculated plan above works without it.