This calculator provides educational information based on published circadian rhythm research. It is not medical advice and should not replace consultation with a healthcare provider.
If you have medical conditions, take medications, are pregnant, or have concerns about travel health, please consult your doctor before following any jet lag prevention strategies, especially melatonin use.
The Science Behind It
Your body has an internal 24-hour clock called the circadian rhythm. This clock controls when you feel sleepy, alert, hungry, and more. It's primarily regulated by the suprachiasmatic nucleus (SCN) in your brain.
When you cross time zones, your internal clock is suddenly out of sync with the local time. Your body thinks it's one time while the sun and local schedule say otherwise. This mismatch causes jet lag symptoms like fatigue, poor sleep, and difficulty concentrating.
Key Fact:
Without intervention, your circadian rhythm adjusts at about 1 hour per day for eastward travel and 1.5 hours per day for westward travel. A 6-hour time change could take 4-6 days to fully adjust!
The Body Temperature Minimum is a specific time in your sleep cycle when your core body temperature reaches its lowest point. This typically occurs 2-3 hours before your natural wake time.
MinT is the anchor point of your circadian rhythm. It's the reference we use to calculate when you should seek or avoid light to shift your body clock.
How We Calculate Your MinT:
- • If you sleep 7 hours or less: MinT = Wake time - 2 hours
- • If you sleep more than 7 hours: MinT = Wake time - 3 hours
Example: If you wake at 7:00 AM after 8 hours of sleep, your MinT is 4:00 AM.
Light is the most powerful tool for resetting your circadian rhythm. But timing is everything! The Phase Response Curve shows how light exposure affects your body clock depending on when you're exposed to it.
☀️ Light AFTER your MinT → Phase Advance (shifts earlier)
Seeing bright light after your MinT tells your body "wake up earlier tomorrow." This is perfect for eastward travel.
🌙 Light BEFORE your MinT → Phase Delay (shifts later)
Seeing bright light before your MinT tells your body "stay up later tonight." This works for westward travel.
Critical: Getting light at the wrong time can shift you in the opposite direction, making jet lag worse! This is called antidromic re-entrainment.
How the Calculator Works
We calculate the time zone difference between your origin and destination, determine the direction of travel (eastward or westward), and identify the number of time zones you'll cross.
Special case: For trips crossing more than 12 time zones, we evaluate whether it's easier to adjust by going in the opposite direction (e.g., 14 hours west instead of 10 hours east).
Based on your normal sleep schedule, we determine your current Body Temperature Minimum. This becomes the foundation for all timing calculations.
Using the Phase Response Curve, we calculate 4-hour windows for when you should seek or avoid light:
Eastward Travel (Phase Advance)
AVOID light 4 hours before MinT → SEEK light 4 hours after MinT
Westward Travel (Phase Delay)
SEEK light 4 hours before MinT → AVOID light 4 hours after MinT
We shift your MinT gradually (1 hour/day for east, 1.5 hours/day for west) and create a day-by-day plan showing:
- Adjusted sleep times
- Light exposure windows
- Melatonin timing (for eastward travel)
- Specific actions to take
The plan typically starts 3 days before departure and continues for several days after arrival, depending on the number of time zones crossed.
Why This Approach Works
Research-Based
Our formulas are derived from peer-reviewed studies on circadian rhythms and jet lag management, including work by Burgess, Eastman, and other leading chronobiology researchers.
Pre-Adaptation
By starting 3 days before travel, you can pre-shift your rhythm by 2-3 hours. Studies show this can reduce jet lag severity by 60% or more.
Precise Timing
Unlike generic "get morning sunlight" advice, we tell you exactly when to seek or avoid light based on YOUR specific sleep schedule and MinT.
Personalized
Every person's circadian rhythm is slightly different. We calculate based on your actual sleep times, not population averages.
Limitations & Important Notes
This calculator cannot account for:
- Individual variations in circadian rhythm sensitivity
- Age-related differences in adjustment speed
- Effects of medications on your sleep-wake cycle
- Pre-existing sleep disorders
- Factors like stress, alcohol, caffeine, or illness
- Multiple-leg trips with layovers in different time zones
Actual results may vary. Some people adjust faster or slower than average. The plan provides scientifically sound guidance, but perfection is not guaranteed.