Jet Lag Calculator
Last updated: 2026-06-25
Jet lag recovery depends on the time difference between your origin and destination and the direction you travel, and usually takes about one day per hour of difference.
Traveling east (time moves earlier) is harder to adjust to than traveling west.
Enter Time Zones
Estimated Recovery Time
0 days
- Time difference
- Travel direction
- Destination local time (vs. now)
The recovery days are a simplified estimate based on the rule of about one day per hour of difference, and are not a medical diagnosis. Use for fun and reference only.
How to use it
- Select your origin time zone — Select the time zone where you currently live (e.g., Seoul, UTC+9).
- Select your destination time zone — Select the time zone of your travel destination.
- Review the result — Click Calculate to see the time difference, direction, estimated recovery days, and light tips.
Jet lag and how adjustment works
Jet lag happens when you cross several time zones quickly and your internal body clock (circadian rhythm) falls out of sync with local time, causing fatigue, insomnia, and loss of appetite. The time needed to adjust depends on the size of the time difference and the direction of travel.
| Direction | Change | Difficulty | Recommended light |
|---|---|---|---|
| Eastward | Time moves earlier (advance) | Harder (≈ difference × 1 day) | Morning light |
| Westward | Time moves later (delay) | Relatively easier (≈ difference × 0.7 day) | Evening light |
The human body clock naturally runs slightly longer than 24 hours, so it adapts well to lengthening the day (west, going to bed later) but takes longer to advance (east, going to bed earlier). That is why this calculator multiplies the time difference by about 1x for eastward travel and about 0.7x for westward travel to estimate recovery days.
How to adjust faster — On arrival, immediately shift your meals and sleep to local time, and get plenty of daylight. If you traveled east, morning light helps; if you traveled west, evening light helps reset your body clock. Staying hydrated and taking short naps also help.
Frequently Asked Questions (FAQ)
How many days does it take to recover from jet lag?
A common rule of thumb is about one day of recovery per hour of time difference. However, traveling east (time moves earlier) is harder to adjust to than traveling west. This calculator applies roughly 1x the time difference for eastward travel and about 0.7x for westward travel. Individual differences are large, so use it for reference only.
Why is eastward travel harder?
The human body clock naturally runs slightly longer than 24 hours, so it adapts fairly well to lengthening the day (traveling west, going to bed later). Traveling east means going to bed and waking up earlier, which is harder because it requires advancing your body clock. That is why the same time difference feels more tiring when traveling east.
Are there ways to adjust to jet lag faster?
Immediately match your meals and sleep to the destination's local time, and get plenty of daylight to reset your body clock. If you traveled east, use morning light; if you traveled west, use evening light. On the first day, limit caffeine and naps and stay well hydrated.
Are the recovery days from this calculator accurate?
The recovery days are a simplified estimate based on the common rule of about one day per hour of time difference, and are not a medical diagnosis. Results vary greatly with age, health, sleep habits, and flight time, so use them for fun and reference only.
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Last updated: 2026-06-25