Jet Lag Calculator
Estimate hour shift and recovery days for a trip between two time zones.
Written by Golam Rabbani, Founder & Lead Engineer
How to use this jet lag calculator
- Pick the origin time zone (where you are starting).
- Pick the destination time zone.
- Enter the departure date and time in the origin local time.
- Press "Calculate jet lag".
- Read the hour shift, direction, estimated recovery days, and the matching local times at both ends.
- Use Copy to share the result or Reset to start over.
About this jet lag calculator
Jet lag is what happens when your circadian rhythm lags behind the local clock at your destination. This tool estimates the size of the shift in hours, the direction (eastward or westward), and a rough recovery estimate based on the common rule of thumb that westward travel recovers about 1.5 hours per day and eastward travel about 1 hour per day.
It works by taking the departure moment, expressing it as an absolute UTC timestamp using your origin zone’s current offset, then asking the same instant what time it would be in the destination zone. The signed difference is the hour shift; positive means the destination is ahead (eastward feel), negative means behind (westward feel). Recovery days are <code>|shift| ÷ factor</code>, where factor is 1.0 for eastward and 1.5 for westward.
Worked example: origin Europe/London, destination Asia/Tokyo, departing 28 May 2026 at 10:00 London time. The tool reports an 8-hour shift eastward, an estimated 8 days of recovery, and shows the matching destination wall-clock time (18:00 in Tokyo on the same calendar day). Useful for planning when to arrive, when to sleep, and how aggressively to shift bedtimes before the trip.
The recovery figure is a rule of thumb, not medical advice — actual jet lag depends on light exposure, sleep quality, age, caffeine, and individual chronotype.
FAQ
- Why is eastward harder than westward?
- Most people’s natural circadian rhythm runs slightly longer than 24 hours, so it is easier to delay (westward) than to advance (eastward) the sleep cycle. The 1.5 vs 1.0 ratio reflects this.
- Does this account for DST?
- Yes — the offset is sampled at the departure moment, so if either zone is in DST on that date the shift reflects it.
- Is the recovery time guaranteed?
- No. It is a rough estimate; people recover faster with light exposure, hydration, and short scheduled naps. Talk to a doctor for medication or shift-work concerns.
- Why does the tool ask for departure time in origin local time?
- It is the time you would actually read on your watch at the airport. The tool converts it to the destination zone so you can plan around when you land.