Travel

Jet Lag Calculator

Calculate jet lag severity, recovery time, and get a personalized light exposure and melatonin schedule.

Quick Answer

Jet lag recovery takes roughly 1 day per timezone crossed when traveling east, and about half that when traveling west. Eastward travel is harder because it requires advancing your body clock (going to sleep earlier), which is more difficult than delaying it. Light exposure timing is the most powerful tool for resetting your circadian rhythm.

Jet Lag Assessment

Time Difference
5h
Eastward
Recovery Time
5
days (estimated)
Severity
Moderate

Light Exposure Schedule

☀Seek bright light in the morning at your destination
☀Avoid light in the late afternoon/evening
☀Shift your sleep 1 hour earlier per day for 3 days before departure
☀Use sunglasses in the afternoon to block light cues

Melatonin Timing

Take 0.5-3mg melatonin at local bedtime (the night of arrival). Avoid taking it during daylight hours.

About This Tool

Jet lag (medically known as desynchronosis) occurs when your internal circadian clock is misaligned with the local time at your destination. Your body's master clock, located in the suprachiasmatic nucleus of the hypothalamus, regulates sleep-wake cycles, hormone release, body temperature, and digestion on roughly a 24-hour rhythm. Crossing multiple time zones disrupts this rhythm, causing the familiar symptoms of fatigue, insomnia, digestive issues, and cognitive impairment.

Why Eastward Travel Is Harder

Traveling east requires advancing your circadian clock (going to sleep earlier than your body wants), while westward travel requires delaying it (staying up later). The human circadian clock naturally runs slightly longer than 24 hours, making it inherently easier to delay than advance. Research consistently shows that eastward travelers experience more severe symptoms and take 25-50% longer to adjust.

The Science of Light Therapy

Light is the most powerful zeitgeber (time-giver) for the circadian system. Bright light exposure suppresses melatonin production and signals wakefulness to the brain. Strategic light exposure at specific times can shift your circadian clock by 1-2 hours per day. For eastward travel, morning light at the destination advances your clock. For westward travel, evening light delays it. Getting the timing wrong can actually worsen jet lag by shifting your clock in the wrong direction.

Recovery Timeline

Most people adjust at a rate of about 1-1.5 timezones per day. A 6-hour eastward shift might take 5-6 days for full recovery, while the same westward shift takes 3-4 days. Age, fitness level, and individual chronotype all influence recovery speed. Younger travelers and those who exercise regularly tend to adjust faster. Night owls adjust to westward travel more easily, while early birds do better with eastward trips.

Frequently Asked Questions

Does melatonin actually help with jet lag?
Yes. A Cochrane review of 10 studies found melatonin significantly reduces jet lag when taken close to target bedtime at the destination. Doses of 0.5-5mg are effective, with 0.5mg working nearly as well as higher doses with fewer side effects. Take it 30 minutes before your desired bedtime at the destination.
Should I try to adjust my sleep before departure?
For trips crossing 3 or fewer timezones, pre-adjustment isn't necessary. For larger shifts, gradually moving your bedtime 1 hour per day toward the destination time for 2-3 days before departure can help. Full pre-adjustment is impractical for shifts greater than 4-5 hours.
Is it better to nap or stay awake on arrival?
If you arrive during daytime, try to stay awake until local bedtime to force your clock to adjust. If you must nap, limit it to 20-30 minutes before 3 PM local time. A long afternoon nap will make it harder to sleep at night and prolong your jet lag.
Do sleeping pills help with jet lag?
Sleeping pills can help you sleep on the plane and on the first night, but they do not reset your circadian clock. They may mask jet lag symptoms without addressing the underlying clock misalignment. If used, short-acting formulations are preferred. Combine with light therapy for actual circadian adjustment.
Can frequent flyers become immune to jet lag?
No. Research on flight crew and frequent travelers shows that chronic jet lag does not lead to immunity. In fact, it may lead to long-term health effects including cognitive impairment, increased cancer risk, and metabolic disorders. Frequent flyers can become better at managing symptoms, but the circadian disruption still occurs.

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