Jet Lag Calculator
Beat jet lag day by day
Enter your departure and destination timezones, we'll build a personalized adjustment plan with sleep timing, light exposure, and behavior tips.
The science of jet lag in 60 seconds
Your body has an internal clock, a master oscillator in the brain\'s suprachiasmatic nucleus (SCN), that anchors a ~24-hour rhythm. This clock isn\'t fixed by the sun; it\'s only entrained by light. When you fly across timezones, your internal clock is suddenly out of sync with the local light-dark cycle. Every cell in your body, including those governing hormone release, body temperature, and gut function, gets a confusing signal.
The result: insomnia at night, sleepiness during the day, digestive issues, brain fog, and impaired physical performance. The clock does reset itself, through light exposure at the new location, but it takes time, roughly one day per timezone crossed.
Westward vs eastward
The two directions are not equal:
- Westward (e.g., London → New York): You\'re extending your day. Your clock is delaying, staying up later, sleeping in longer. This aligns with your body\'s natural tendency (your intrinsic circadian period is slightly over 24 hours), so it\'s easier. Plan to stay up to local bedtime on arrival; get late-afternoon and early-evening light.
- Eastward (e.g., New York → London): You\'re compressing your day. Your clock has to advance, go to bed earlier, wake up earlier. This works against your body\'s tendency, so it\'s typically 50% slower. Plan to seek bright morning light at the destination immediately; avoid late-evening light. Consider melatonin 0.5–3 mg 30 min before target bedtime (consult a doctor first).
The light-exposure protocol
Light is by far the most potent circadian reset. Use it strategically:
- Identify your "minimum body temperature" time (Tmin). Roughly 2 hours before your usual wake time at home. So if you wake at 7 AM, your Tmin is ~5 AM home time.
- Light after Tmin advances your clock (makes you sleep earlier the next night), useful for eastward travel.
- Light before Tmin delays your clock (makes you sleep later), useful for westward travel.
- 15+ minutes of natural sunlight is the gold standard. Bright indoor light (10,000 lux therapy lamps) works in winter or if you can\'t get outside.
- Avoid light in the wrong window. The reverse rules apply: avoid light at the time of day that would push your clock the wrong direction. Use sunglasses outdoors during these windows if needed.
Pre-adjusting before you fly
The most effective jet lag strategy starts before you board. For trips of three or more time zones, shifting your sleep schedule by an hour a day toward your destination's time, for three days before departure, can cut your recovery time dramatically. Pair the shift with light: for eastward travel, get bright light earlier each morning and dim your evenings; for westward travel, do the opposite. Arriving partially adjusted beats crashing into a new schedule cold. For short trips of one or two days, pre-adjusting usually isn't worth it, you'll be home before your body fully shifts.
Light is your most powerful tool
Bright light is by far the strongest signal for resetting your body clock, stronger than melatonin, meal timing, or exercise. The catch is that timing it wrong pushes your clock the wrong way. The rule of thumb hinges on your body-temperature low point, roughly two hours before your usual wake time:
- Eastward travel (e.g. US to Europe): seek bright morning light at your destination and avoid light in the late evening. You're advancing your clock.
- Westward travel (e.g. Europe to US): seek afternoon and early-evening light, and avoid bright light first thing in the morning. You're delaying your clock.
The day-by-day plan above already accounts for your direction of travel.
Does melatonin help?
For eastward travel across five or more time zones, a low dose of melatonin (0.5–3 mg) taken close to your target bedtime at the destination can speed adjustment, the timing matters far more than the dose, and bigger doses don't work better. It's less useful for westward travel, where light does most of the work. Melatonin is widely available but isn't right for everyone, so check with a doctor first, especially if you take other medications. Whatever you do, light exposure remains the foundation; melatonin is a supporting player, not a substitute.
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Frequently Asked Questions
How long does it take to recover from jet lag?
Rule of thumb: about one day per timezone for westward travel, 1.5 days per zone for eastward (eastward is harder because your body has to compress its circadian rhythm). A trip across 6 timezones eastward typically takes 9 days to fully adjust; westward, about 6 days. Some people adjust faster, others slower, sleep quality, age, and pre-trip preparation all matter.
Why is eastward jet lag worse than westward?
Your intrinsic circadian rhythm runs slightly longer than 24 hours (most people: 24.2 hours). This means delaying your clock (westward) is naturally easier, you're working with your body's tendency. Advancing your clock (eastward) fights it. Most controlled studies show east is ~50% slower to adjust than west.
Does melatonin help with jet lag?
Yes, when timed correctly. Multiple meta-analyses show melatonin (0.5–3 mg) taken close to target bedtime at the destination accelerates circadian adjustment for east-to-west flights of 5+ timezones. The dose matters less than the timing. Don't use long-acting formulations. Talk to a doctor first, especially if you take other medications.
What's the most important thing for managing jet lag?
Light exposure timing. Bright light is the strongest signal that resets your circadian rhythm, much stronger than meal timing, exercise, or melatonin. For eastward travel, get bright morning light at the destination and avoid evening light. For westward travel, get afternoon/evening light and avoid early morning light. The general rule: light during the "biological day" advances your clock; light during the "biological night" delays it.
Should I shift my schedule before traveling?
For short trips (1–3 days), it's often not worth it. For longer trips, shifting your bedtime by 1 hour per day in the destination's direction for 3 days before travel helps significantly. Pair this with bright-light exposure aligned to your new wake time. Pre-adapting is much easier than crashing into a new schedule on arrival.
Does staying awake on the plane help?
Depends on your flight timing. If you'll arrive in the morning local time, try to sleep on the plane (it's "night" at the destination). If you'll arrive in the evening, stay awake (it's still "day"). Match your in-flight behavior to destination local time, not departure time.
Does the "starve and feast" diet really work?
The Argonne anti-jet-lag diet involves alternating fasting and feasting days before travel. Evidence is limited and inconsistent. Meal timing does influence circadian rhythm (especially peripheral clocks in liver and other organs), but probably less than light. A simpler approach: eat at destination meal times as soon as you arrive, avoid heavy meals close to local bedtime, and skip in-flight meals that conflict with the new schedule.