Jet Lag Recovery Calculator
Estimate how many days you'll need to recover from jet lag based on time zones crossed, travel direction, and age. Use it before a trip to plan adjustment strategies.
About this calculator
Jet lag recovery time depends on how many time zones you cross, the direction of travel, and individual factors like age. The formula used here is: Recovery Days = timeZoneDiff × (direction === 'east' ? 1.5 : 1) × (age > 50 ? 1.2 : 1). Eastward travel is harder because it requires advancing your circadian clock (going to bed earlier), which the human body does more slowly than delaying it — hence the 1.5× multiplier. Older adults (50+) adapt more slowly due to reduced circadian plasticity and lower melatonin amplitude, reflected by the 1.2× age factor. As a general rule of thumb without adjustments, the body re-entrains at roughly one time zone per day. This calculator refines that estimate for your specific situation so you can plan light exposure, melatonin timing, and meal schedules accordingly.
How to use
A 55-year-old traveller flies from New York to London, crossing 5 time zones eastward. Step 1 — Base calculation: 5 time zones. Step 2 — Direction multiplier (east): 5 × 1.5 = 7.5. Step 3 — Age multiplier (age > 50): 7.5 × 1.2 = 9.0 days. Expected recovery time is approximately 9 days. To shorten this, the traveller should seek morning light upon arrival, take 0.5 mg melatonin at the new local bedtime starting the day before departure, and avoid naps longer than 20 minutes during the adjustment period.
Frequently asked questions
Why is eastward jet lag worse than westward jet lag?
Your internal circadian clock has a natural free-running period of approximately 24.2 hours, meaning it slightly prefers to run long and delay rather than advance. Westward travel asks you to stay up later (delay your clock), which aligns with this natural tendency and is relatively easy. Eastward travel requires you to go to sleep and wake up earlier (advance your clock), which fights against the natural drift and takes about 50% longer to adjust per time zone. This asymmetry is well-documented in sleep research and is why many travellers find the return journey easier after an eastward trip.
How does age affect jet lag severity and recovery time?
Older adults (roughly 50 and above) experience more severe and prolonged jet lag for several reasons. The amplitude of the circadian pacemaker (suprachiasmatic nucleus) weakens with age, making it less responsive to light cues that drive re-entrainment. Melatonin secretion also declines with age, reducing the hormonal signal that synchronises peripheral clocks throughout the body. Additionally, older adults are more likely to have pre-existing sleep disorders that compound jet lag symptoms. The 1.2× multiplier in this calculator reflects the average additional recovery time observed in older travellers.
What are the most effective strategies to speed up jet lag recovery?
The three most evidence-backed strategies are timed light exposure, strategic melatonin supplementation, and meal timing. Bright light at the right local time is the strongest resynchroniser of the circadian clock — seek morning light for eastward travel and evening light for westward travel. Low-dose melatonin (0.5 mg) taken at the target destination's bedtime for the first few days accelerates clock shifting without the grogginess associated with higher doses. Eating meals on the destination's local schedule also helps entrain peripheral clocks in the liver and gut. Avoiding alcohol and keeping caffeine to mornings only further supports faster adaptation.