Key Takeaways
- Jet lag occurs when your internal clock is misaligned with the local time at your destination.
- Eastward travel (earlier time zones) is generally harder to adjust to than westward travel.
- Light exposure is the most powerful tool for resetting your circadian clock when traveling.
What causes jet lag?
Jet lag happens when you cross multiple time zones faster than your internal circadian clock can adjust. Your body remains on its original schedule while the external environment has shifted.
Symptoms include fatigue, insomnia, difficulty concentrating, digestive issues, and general malaise. The severity depends on the number of time zones crossed and travel direction.
Eastward vs westward travel
Westward travel (flying west) is generally easier because it requires delaying your internal clock, which the body does naturally. You stay up later and wake later, which feels more natural.
Eastward travel (flying east) is harder because it requires advancing your clock — going to bed earlier and waking earlier. This goes against the body's natural tendency to delay, so it takes more discipline and light management.
Light exposure guidelines
Light is the strongest cue for circadian reset. After eastward travel, seek bright morning light to help advance your clock. After westward travel, seek evening light to help delay your clock.
Avoid bright light at the wrong time: after eastward travel, avoid late-afternoon and evening bright light. After westward travel, avoid early-morning bright light. Use sunglasses or dim indoor lighting when needed.
Gradual schedule shifting
Adjusting your sleep schedule before travel can reduce jet lag. Shift bedtime and wake time by 15-30 minutes per day toward your destination time zone, counting those days back from your travel date.
Once at your destination, adopt the local schedule immediately — eat meals and sleep according to local time. Short naps (20-30 minutes) can help, but long naps may interfere with nighttime sleep.
Melatonin and medications
This calculator does not provide melatonin dosing advice. Melatonin supplements can help with jet lag, but dosage timing is critical, and quality varies by country and manufacturer. Consult a healthcare provider before using melatonin.
Some prescription medications are available for severe jet lag, but they should only be used under medical supervision. The non-pharmacological approaches — light timing and schedule planning — are effective for most travelers.