What is jet lag?

Jet lag is a temporary sleep disorder that occurs when your body's internal clock (circadian rhythm) is out of sync with the time zone you're in. It happens after traveling across multiple time zones, causing symptoms like fatigue, insomnia, difficulty concentrating, digestive issues, and general malaise. Your body naturally operates on a roughly 24.2-hour cycle, regulated by light exposure and other environmental cues called "zeitgebers."

Why is eastward travel harder than westward?

Because the human circadian rhythm runs slightly longer than 24 hours, it's naturally easier to delay sleep (stay up later) than to advance it (go to bed earlier). When traveling east, you need to fall asleep earlier than your body expects—a process called phase advancement. Westward travel requires phase delay, which aligns better with our natural tendency. Research shows eastward travel typically requires about 1 day of recovery per time zone crossed, while westward travel needs only about 0.67 days per zone.

How does age affect jet lag recovery?

Studies consistently show that circadian rhythm flexibility decreases with age. Younger travelers (under 30) typically recover at baseline rates, while adults over 50 may need 25-50% more time to fully adjust. This is due to reduced melatonin production and less responsive circadian mechanisms in older individuals.

Tool description

This jet lag recovery calculator estimates how long it will take your body to fully adjust after traveling across time zones. It uses scientifically-backed formulas based on research from sleep medicine and chronobiology. The calculator considers three key factors: the number of time zones crossed, the direction of travel (east or west), and your age—all of which significantly impact recovery time.

You can input time differences manually or select specific origin and destination time zones for automatic calculation. The tool also provides personalized recovery tips based on your travel direction and age, including optimal light exposure timing and sleep schedule adjustments.

Features

  • Two input modes: Enter hours manually or select from a comprehensive list of world time zones
  • Direction-aware calculations: Accounts for the asymmetry between eastward and westward travel
  • Age-adjusted estimates: Applies research-based age factors for more accurate predictions
  • Automatic timezone detection: Pre-fills your current timezone as the origin
  • Science-based recovery tips: Provides actionable advice on light exposure, melatonin timing, and sleep scheduling

Use cases

  • Planning recovery time after an international business trip to schedule important meetings appropriately
  • Preparing for a vacation by understanding how many days you'll need before feeling fully adjusted
  • Athletes and performers calculating optimal arrival times before competitions or events
  • Frequent travelers optimizing their schedules to minimize jet lag impact
  • Healthcare providers advising patients on travel recovery expectations