How Long to Recover and How to Adapt
Last reviewed: January 2026
A jet lag calculator estimates recovery time and provides a light exposure schedule to help you adjust to a new time zone. It factors in the number of time zones crossed, travel direction, and your chronotype to create a personalized adaptation plan.
The body adjusts roughly 1–1.5 hours per day eastward, 1 hour per day westward. Eastward travel is harder because it requires advancing your circadian clock. Best strategies: Start adjusting your sleep schedule 2–3 days before departure. Get light exposure in the morning at your destination. Avoid alcohol and caffeine on the flight. Stay hydrated. Melatonin (0.5–3mg) taken at destination bedtime for the first few nights can help. Avoid naps longer than 20 minutes on arrival day.
| Time Zones Crossed | Recovery Time | Severity | Direction |
|---|---|---|---|
| 1–3 | 1–2 days | Mild | Either |
| 4–6 | 3–5 days | Moderate | Worse eastbound |
| 7–9 | 5–8 days | Significant | Worse eastbound |
| 10–12 | 7–12 days | Severe | Comparable both ways |
Jet lag (circadian desynchrony) occurs when your internal biological clock is misaligned with the local time at your destination. The human circadian rhythm is regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus, which uses light input from the retina to maintain an approximately 24-hour cycle of sleep-wake, hormone release, body temperature, and metabolic processes. When you cross time zones rapidly by air, your SCN remains set to your origin time zone and must gradually shift to the new local time. This adjustment takes approximately 1-1.5 days per time zone crossed — a six-hour eastward shift (New York to Paris) typically requires 6-9 days for full circadian realignment.
Eastward travel is harder than westward travel because the human circadian clock naturally runs slightly longer than 24 hours (approximately 24.2 hours for most people). Traveling west "lengthens" the day, which aligns with the clock's natural tendency. Traveling east "shortens" the day, fighting against it. A flight from Los Angeles to Tokyo (crossing 8 time zones westward, losing 8 hours from the day) typically produces less severe jet lag than the return flight (gaining 8 hours eastward). Studies show that eastward adaptation takes about 50% longer than westward adaptation for the same number of time zones, and symptoms are correspondingly more intense.
Light exposure is the most powerful tool for shifting circadian rhythms. To adjust to an earlier time zone (eastward travel), seek bright light in the morning at your destination and avoid it in the evening. To adjust to a later time zone (westward travel), seek evening light and avoid morning light. The timing is critical: light exposure at the wrong circadian phase can shift the clock in the wrong direction, worsening jet lag. As a practical rule, for eastward travel of 6 or fewer time zones, get morning light immediately upon arrival. For eastward travel exceeding 6 time zones, the shift is so large that the body may interpret morning light as evening light and shift the wrong way — in these cases, avoid light for the first few hours after arrival and begin light exposure in the late morning.
Melatonin supplementation can complement light exposure therapy. Taking 0.5-3 mg of melatonin at the target bedtime in the new time zone, starting the first evening after arrival, signals the brain that it is nighttime and promotes sleep. Taking melatonin too early or in too high a dose can cause grogginess and paradoxically worsen adaptation. Hydration during the flight matters because the low humidity in pressurized aircraft cabins (typically 10-20% relative humidity versus 30-60% at home) causes dehydration that exacerbates fatigue and cognitive impairment already caused by circadian disruption. Caffeine is useful for maintaining alertness during destination daytime hours but should be avoided within 6-8 hours of the target bedtime to prevent interference with the sleep shift.
For trips shorter than 48-72 hours, adapting to the destination time zone may not be worthwhile — you begin adjusting just in time to return home and face reverse jet lag. Instead, many frequent business travelers maintain their home time zone as much as possible: scheduling meetings during what would be their normal waking hours back home, eating meals at home-time intervals, and sleeping at home-time night. This "anchor sleep" strategy works best when the time zone difference is 3-5 hours and business meetings can be accommodated within the overlap of the two schedules. For longer trips or larger time shifts, a gradual pre-adjustment of 1 hour per day starting 3-4 days before departure can reduce the adjustment needed upon arrival by half.
Professional sports teams traveling across multiple time zones face measurable performance decrements. Research published in sports science journals has found that MLB teams traveling eastward lose approximately 3-4% more games than expected based on team quality, with the effect largest for teams crossing 3+ time zones. The NFL accounts for this by scheduling West Coast teams playing 1 PM Eastern games (which feel like 10 AM to the players' circadian systems) earlier in the season when possible. Olympic athletes traveling to competitions often arrive 1-2 weeks early to acclimate, using structured light exposure, melatonin protocols, and graduated training schedules. Cognitive performance — reaction time, decision-making speed, and tactical awareness — degrades 5-15% during the first 48-72 hours after crossing 6+ time zones, which in elite sports can mean the difference between medaling and missing the podium.
Jet lag occurs because your circadian rhythm (internal body clock) is misaligned with the local time zone. Light exposure is the most powerful tool for resetting it. For eastward travel, seek bright morning light and avoid evening light to advance your clock. For westward travel, seek evening light and avoid morning light to delay it. Melatonin (0.5–3mg) taken at the destination's bedtime accelerates adjustment. The body adapts at roughly one time zone per day — a 6-hour shift takes about a week to fully resolve. Pre-shifting your sleep schedule by 1–2 hours in the days before departure reduces the adjustment needed upon arrival.
See also: Sleep Calculator · Sleep Debt Calculator · Time Zone Converter
→ Eastward travel is harder than westward — your body prefers longer days. The human circadian clock naturally runs slightly longer than 24 hours, making it easier to stay up later (westward adjustment) than wake up earlier (eastward). Flying east from LA to London (8 hours ahead) takes longer to recover from than flying west from London to LA.
→ Start shifting your sleep schedule 2–3 days before departure. Move your bedtime and wake time by 30–60 minutes per day toward the destination time zone. Even a partial shift reduces jet lag severity. This strategy works best for trips crossing 3+ time zones. Use our Time Zone Converter to plan your shift schedule.
→ Light exposure is the most powerful circadian reset tool. Bright light in the morning advances your clock (useful for eastward travel). Bright light in the evening delays it (useful for westward). Avoid bright light at the wrong time — wearing sunglasses strategically on arrival can prevent your clock from shifting in the wrong direction.
→ Melatonin timing matters more than dose. Take 0.5–3mg of melatonin 30 minutes before your target bedtime in the new time zone. Higher doses aren't more effective and can cause grogginess. For eastward travel, start taking melatonin at the destination's bedtime the night before departure. See our Sleep Debt Calculator to assess your baseline.
See also: Time Zone Converter · Sleep Debt Calculator · Travel Budget Calculator · Meeting Time Planner