Jet Lag Calculator
Enter departure and arrival time zones to calculate the time difference and generate a personalized schedule to help your body adapt faster.
The adaptation schedule is a general reference based on sleep science. If you have a sleep disorder or health condition, consult a healthcare professional.
Jet Lag Summary
Departure Time Zone
Seoul / Busan / Jeju - Korea Time
UTC+9
Arrival Time Zone
New York / Washington D.C. / Boston - US Eastern Time
UTC-4
11h
Time Difference
Direction
~11d
Est. Recovery
Adaptation Schedule
3 day(s) before
Go to bed earlier to prepare for the eastward shift
Shift bedtime by up to 1 hour(s) per day
2 day(s) before
Go to bed earlier to prepare for the eastward shift
Shift bedtime by up to 1 hour(s) per day
1 day(s) before
Go to bed earlier to prepare for the eastward shift
Shift bedtime by up to 1 hour(s) per day
Departure day
Limit sleep on the flight and stay active to align with local daytime at destination
1 day(s) after arrival
Get bright morning sunlight to advance your body clock
2 day(s) after arrival
Get bright morning sunlight to advance your body clock
This schedule is a general guideline. Actual recovery depends on age, health, and individual sleep patterns.
Usage Tips
Start adjusting your sleep schedule 23 days before departure
The larger the time difference, the more your body benefits from preparation before you leave. Traveling east? Go to bed about an hour earlier each day. Heading west? Push bedtime a little later. After arrival, timed light exposure is the most effective way to reset your body clock. Consider caffeine timing as well — avoid it in the evening when traveling east. Melatonin can help too, but talk to a doctor about dosage and timing.
What is Jet Lag Calculator?
The Jet Lag Calculator is a scientific travel planner designed to mitigate Jet Lag (Circadian Desynchrony) caused by crossing multiple time zones. By analyzing the precise offset between your origin and destination, it maps how your body's internal clock responds to directional shifts (Eastward or Westward). The tool generates a structured pre-travel sleep adjustment schedule (Bedtime Shifting) and post-arrival light exposure strategies to accelerate your circadian resynchronization and prevent excessive travel fatigue.
How to Use
- 1Select your departure city (Origin time zone) and destination city (Arrival time zone) from the provided dropdown menus.
- 2Input your exact departure date and the estimated flight duration in hours.
- 3Instantly review the jet lag metrics: absolute time difference, normalized direction (Eastward or Westward), and the estimated recovery timeline.
- 4Follow the calculated day-by-day adaptation guide to adjust your sleep schedule prior to departure and manage outdoor light exposure upon arrival.
- 5Utilize natural sunlight at your destination according to the guide to regulate melatonin production and keep your bedtime routine in check.
- 6Use the 'Copy Results' feature to save your customized sleep schedule to your mobile notes or calendar app for easy reference during travel.
Read jet lag through time difference, direction, and recovery days
Last reviewed: July 11, 2026Time-zone difference and adaptation
normalized time difference = arrival UTC offset − departure UTC offset; estimated recovery days = round(|time difference hours|)
The calculator compares date-aware IANA offsets, identifies east or west travel, and applies a conservative one-day-per-hour reference for recovery.
Traveling from London to New York
- • Departure Europe/London
- • Arrival America/New_York
- • Reference date July 11, 2026
- 1. The seasonal offset difference normalizes to about −5 hours
- 2. Direction is west and estimated recovery is round(5) = 5 days
The trip is shown as about five hours west with a five-day reference recovery period.
How to read the result
- Westward travel shifts the suggested sleep later, while eastward travel shifts it earlier.
- Pre-travel steps for up to three days and post-arrival light notes turn the time difference into a practical routine reference.
Conditions that change the result
- DST and the chosen reference date can change a city's UTC offset.
- Recovery days are a planning estimate and do not measure sleep, light exposure, caffeine, flight fatigue, or individual adaptation.
Common input mistakes
- Using a fixed city difference without the travel date can miss daylight-saving changes.
- Do not treat melatonin or sleep medication suggestions as a personal prescription; ask a professional when needed.
Reference Knowledge
- ●The internal circadian pacemaker naturally synchronizes with the Earth's rotation, typically requiring approximately one day of adjustment for each time zone hour crossed.
- ●Because the human biological clock has an intrinsic cycle of about 24.2 hours, pushing sleep later (Westward travel) is physically easier than advancing it earlier (Eastward travel).
- ●Strategic exposure to natural bright light (blue-wavelength light) at the destination is the most potent external cues (zeitgeber) for resetting the brain's internal master clock.
- ●Maintaining high hydration levels and limiting alcohol or caffeine during flight reduces overall cabin-induced fatigue, indirectly easing cellular resynchronization.
FAQ
Q.Why is adjusting to eastward travel more challenging than westward travel?
The human biological master clock (the suprachiasmatic nucleus) runs on a natural internal rhythm slightly longer than 24 hours (about 24.2 hours). Traveling westward effectively lengthens the day, which aligns naturally with our biological tendency to delay bedtime. Conversely, traveling eastward shortens the day, forcing the body to advance its sleep cycle. Advancing the biological clock goes against our natural pacemaker, making eastward recovery feel more difficult and tiring.
Q.How accurate is the estimated recovery timeline?
The standard guideline of one day of recovery per time zone hour crossed is a widely accepted average. However, actual recovery rates vary significantly depending on age, baseline sleep health, cabin environment factors, and post-arrival exposure to sunlight. The estimate serves as a guidance tool rather than a strict medical prediction.
Q.Does shifting my sleep schedule before departure (Pre-shifting) actually work?
Yes, shifting your sleep and wake times by 1 to 1.5 hours daily starting three days before departure gradually nudges your internal pacemaker closer to the destination time. Studies show that this pre-adaptation routine significantly reduces the severity of common jet lag symptoms like brain fog, fatigue, and gastrointestinal issues upon arrival.
Q.Is it better to sleep or stay awake during the flight?
This depends entirely on the local time at your destination when you land. If you land in the morning, you should try to sleep as much as possible on the plane to avoid immediate exhaustion. If you land in the evening, it is better to remain awake during the flight and sleep only when it corresponds to night at your destination.
Q.Can melatonin supplements or sleeping pills help accelerate adaptation?
Taking a low dose of melatonin (0.5mg to 3mg) 30 to 60 minutes before your target bedtime at the destination can signal your brain that night has arrived, promoting faster resynchronization. Prescription sleeping pills, however, should be used with caution and under medical advice due to potential dependency risks and grogginess.
Q.How does screen time from electronic devices affect jet lag?
Blue light emitted from smartphone and computer screens strongly suppresses the natural secretion of melatonin, the sleep hormone. To prevent delaying sleep, avoid screens for at least one hour before your scheduled bedtime. On the flip side, using screens during destination daytime hours can help you stay awake if you are feeling drowsy.
