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Jet Lag Calculator — plan your time zone adjustment.
Compare your departure and arrival time zones. See how many hours your body clock needs to shift, and get a practical day-by-day plan for sleep, light exposure, and caffeine.
Jet Lag Calculator
Plan your adjustment before and after travel.
How to use
Estimate jet lag in three steps.
Pick your locations. Select your departure and arrival cities from preset hubs, search by airport name or IATA code, or pick a fixed UTC offset.
Set your travel details. Choose your travel date and usual sleep schedule. For more precision, expand Advanced mode to enter exact departure/arrival times, pre-trip adjustment days, and trip length.
Review your plan. See the quick answer, estimated adjustment period, and a detailed day-by-day guide for sleep timing, light exposure, caffeine, and naps.
Definition
What is jet lag?
Jet lag is the fatigue and disorientation that follows travel across multiple time zones. Your body's internal clock — the circadian rhythm — is synchronized to your departure time zone and takes time to adjust to the new one.
The severity of jet lag depends primarily on the number of time zones crossed and the direction of travel. Crossing three or more time zones typically produces noticeable symptoms. Crossing six or more can take several days to fully recover from.
This calculator estimates your adjustment period based on the timezone difference between your departure and arrival cities, using the actual DST-aware offsets for your travel date.
Timezone impact
How time zone changes affect your body.
Your circadian rhythm regulates sleep, alertness, hormone production, and body temperature on a roughly 24-hour cycle. When you cross time zones, the external clock shifts but your internal clock doesn't change instantly.
Three key factors determine how quickly you adapt:
- Number of time zones crossed — more zones means a larger shift and longer recovery.
- Direction of travel — eastward travel (losing hours) is generally harder than westward travel (gaining hours) because it is easier to stay up late than to fall asleep early.
- Individual factors — age, sleep habits, and overall health all influence recovery speed.
The calculator uses the first two factors to produce a general estimate. Individual recovery will vary.
Adjustment strategies
Light, sleep, and caffeine guidance.
The calculator's day-by-day schedule is based on three well-known adjustment levers:
Light exposure
Light is the most powerful signal for shifting your circadian clock. After eastward travel, seek bright light in the morning to advance your clock. After westward travel, seek bright light in the late afternoon and evening to delay it. Avoid bright light at the wrong times during the first few days.
Sleep timing
Gradually shift your bedtime toward the destination's local time. The calculator suggests how much to shift each day, working toward full adaptation by the end of the estimated adjustment period.
Caffeine
Caffeine can help maintain alertness during the day but should be limited in the afternoon and evening to avoid interfering with sleep timing. The calculator suggests a cutoff time based on your travel direction.
These are general strategies. For personalized advice, consult a healthcare professional.
FAQ
Frequently asked questions.
How is the jet lag adjustment estimated?
The calculator uses a common heuristic of approximately one adjustment day per three time zones crossed. Eastward and westward travel are treated symmetrically. Planning style (gentle, balanced, faster) adjusts the estimate. This is a general guideline — individual recovery varies based on age, health, and travel habits.
Can I search by airport or city?
Yes. The calculator includes a curated dataset of 100+ major international airports. Search by airport name, IATA code, city, or country. You can also use the timezone dropdowns directly without selecting an airport.
What is the difference between basic and advanced mode?
Basic mode asks for departure/arrival locations, travel date, and sleep schedule — and gives you an instant plan. Advanced mode lets you enter exact departure and arrival times, flight duration, pre-trip adjustment days, trip length, and planning style for a more detailed itinerary.
Does the calculator account for daylight saving time?
Yes. All timezone offsets are calculated using the browser's native IANA timezone database at the exact travel date you select. If DST changes the effective offset between your departure and arrival cities, the calculator uses the correct offset for that date.
What is the difference between eastward and westward jet lag?
When traveling eastward, you lose hours and need to advance your body clock — going to bed and waking up earlier. When traveling westward, you gain hours and need to delay your body clock — staying up later. Eastward travel is generally considered harder because it is easier to stay up late than to fall asleep early.
How does light exposure help with jet lag?
Light is the strongest cue for resetting your internal clock. After eastward travel, seek bright light in the morning to advance your clock. After westward travel, seek bright light in the late afternoon and evening to delay it. The calculator provides direction-aware light timing guidance.
Should I avoid caffeine during adjustment?
The calculator suggests limiting caffeine in the afternoon and evening during the first few days of adjustment. Caffeine can interfere with sleep timing, which is critical when shifting your body clock. This is general guidance — consult a healthcare provider for personalized advice.
Is this medical advice?
No. This calculator provides general travel-planning guidance based on common jet-lag heuristics. It is not a medical diagnostic tool and should not replace professional healthcare advice. Individual recovery varies widely.
Can I share my jet lag calculation?
Yes. Click the Share button to copy a URL that includes your inputs. Open the link to see the same calculation. No data is sent to any server.
What about short trips — should I adjust?
For trips shorter than 2 days, the calculator may suggest maintaining your home schedule rather than fully adapting. Shifting your body clock takes time, and for very short trips the adjustment may cause more disruption than benefit.