Jet Lag Calculator
See how many time zones your trip crosses, which direction is harder, roughly how long it takes to adjust, and what to do about it.
What causes jet lag
Jet lag happens when your internal body clock is still on home time while the world around you runs on a different schedule. The more time zones you cross, the bigger the gap, and it takes a few days for your clock to catch up — shifting roughly an hour per day.
Direction matters: flying east shortens your day and usually feels worse, while flying west lengthens it and is often easier. Once you know the arrival time, plan your trip with the flight time calculator or check the destination on the time zone map. This tool gives a rough estimate and is not medical advice.
Frequently asked questions
How is jet lag calculated?+
From the number of time zones you cross and the direction. Enter origin and destination and it shows zones crossed, east or west, and a rough number of days to adjust.
How long does jet lag last?+
Roughly one day per time zone flying east, and a bit faster flying west — your clock shifts about an hour a day. It varies between people.
Is east or west jet lag worse?+
East is usually harder — it shortens your day and asks you to sleep earlier, which most people find tougher than staying up later.
Does it need my flight details?+
No — just origin and destination cities. No flight number, no API, no personal data.
Is it free?+
Yes — free, no signup, runs in your browser. It is a rough estimate, not medical advice.