Travel Jet Lag Recovery Calculator
Estimate how many days of jet-lag recovery you can expect after a long-haul flight, based on time-zone gap, flight length, age, and travel experience. Use it before booking trips to plan rest days.
Last updated: September 2026
Formula below · 2 sources (iana.org, Wikipedia) · Updated Sep 2026
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About this calculator
Jet lag severity depends on the number of time zones crossed, the direction of travel, flight duration, age, and how frequently a person flies. The formula here is: recovery_days = |shift| × age_factor × travel_frequency × (1 + flight_duration / 24) × direction_factor, where shift = arrival_UTC − departure_UTC taken the short way around the clock (between −12 and +12 hours; New York to Tokyo, +14 hours east, is treated as a 10-hour westward delay) and direction_factor is 1.2 for eastward travel (positive shift) and 0.8 for westward. Research consistently shows westward travel (phase delay) is better tolerated than eastward travel (phase advance) because the human circadian rhythm naturally runs slightly longer than 24 hours, making it easier to stay up late than to fall asleep early. The flight_duration term acknowledges that longer flights compound fatigue independently of time-zone crossing. Age and travel-frequency multipliers let experienced or younger travellers model their personal resilience.
How to use
A 35-year-old frequent flyer (age_factor = 1.0, travel_frequency = 0.7) flies from London (UTC+0) to New York (UTC−5) on a 7-hour flight. Step 1 — shift: −5 − 0 = −5, so 5 zones westward. Step 2 — direction: westward, direction_factor = 0.8. Step 3 — flight term: 1 + 7/24 = 1.292. Step 4 — multiply: 5 × 1.0 × 0.7 × 1.292 × 0.8 ≈ 3.6 recovery days. The return flight eastward (about 8 hours) would give 5 × 1.0 × 0.7 × 1.333 × 1.2 ≈ 5.6 days.
Frequently asked questions
Why does eastward travel cause worse jet lag than flying westward?
The human circadian clock has a natural free-running period slightly longer than 24 hours, making it physiologically easier to delay sleep (stay up later, as in westward travel) than to advance it (sleep earlier, as in eastward travel). The formula reflects this with a direction_factor of 1.2 for eastward flights and 0.8 for westward ones — a 50% difference in predicted recovery time. Strategies like seeking morning light on arrival and avoiding naps can help reset your clock faster after eastward travel.
How does flight duration affect jet lag recovery beyond just time zones crossed?
Even without crossing a single time zone, long flights cause accumulated sleep deprivation, dehydration, reduced cabin pressure, and circadian disruption from altered light exposure. The term (1 + flight_duration / 24) scales recovery time upward for longer flights — a 12-hour flight adds a 50% multiplier compared to a 0-hour baseline. This means a polar route crossing fewer time zones can still produce significant fatigue if the flight is very long.
What lifestyle factors can reduce jet lag recovery time after international travel?
Pre-trip sleep shifting — adjusting bedtime by 1–2 hours in the direction of travel for several days before departure — can meaningfully reduce recovery time. On arrival, exposure to natural daylight, avoiding caffeine after mid-afternoon, and eating meals on local schedule all help re-synchronise your circadian rhythm. The travel_frequency multiplier in this calculator models the fact that frequent flyers develop greater physiological adaptability, reducing their effective recovery days over time.