The Science Behind the Calculator
Research-backed methodology for jet lag prevention and circadian rhythm adjustment
This jet lag calculator is built on decades of peer-reviewed circadian rhythm research. We don't use generic advice—our recommendations are derived from specific scientific formulas and clinical studies on jet lag management.
Below you'll find the key research papers and concepts that inform our calculations, along with explanations of how we apply them to create your personalized plan.
Core Scientific Concepts
The circadian rhythm is controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus. This "master clock" regulates sleep-wake cycles, body temperature, hormone release, and other physiological processes on a ~24-hour cycle.
Key Research:
- • Czeisler et al. (1999) - Human circadian pacemaker studies
- • Duffy & Czeisler (2009) - Effect of light on human circadian physiology
- • Lockley et al. (2003) - Wavelengths of light affecting circadian phase
Core body temperature follows a circadian pattern, reaching its lowest point (MinT) typically 2-3 hours before habitual wake time. This point serves as a stable phase marker for the circadian rhythm.
Our calculator estimates MinT based on your sleep duration and wake time, using established relationships between sleep architecture and temperature rhythms.
Key Research:
- • Lack & Wright (2007) - Chronobiology of sleep in humans
- • Burgess et al. (2003) - Body temperature minimum calculation methods
The PRC describes how light exposure shifts circadian phase depending on when it occurs relative to MinT:
- Light before MinT → Phase delay (shift later)
- Light after MinT → Phase advance (shift earlier)
- Crossover at MinT → Minimal phase shift
This is the fundamental principle we use to calculate when you should seek or avoid light to shift your rhythm in the desired direction.
Key Research:
- • Khalsa et al. (2003) - PRC to single bright light pulses
- • Revell & Eastman (2005) - Advancing human circadian rhythms with light
- • Minors et al. (1991) - PRC for light in humans
Our Calculation Methodology
We calculate 4-hour light exposure windows based on research showing that:
- Light exposure 0-4 hours after MinT produces maximum phase advance
- Light exposure 0-4 hours before MinT produces maximum phase delay
- Light exposure outside these windows has diminishing effects
Supporting Research:
- • Eastman et al. (1994) - Bright light treatment for jet lag
- • Burgess et al. (2002) - Pre-flight phase shifting
- • Revell et al. (2006) - Advancing and delaying sleep schedules
Research shows different adjustment rates depending on travel direction:
Eastward Travel
~1 hour per day adjustment rate (phase advance is harder)
Westward Travel
~1.5 hours per day adjustment rate (phase delay is easier)
Supporting Research:
- • Arendt (2009) - Managing jet lag: Some tricks for pilots
- • Eastman & Burgess (2009) - How to travel the world without jet lag
- • Waterhouse et al. (2007) - Jet lag: trends and coping strategies
For eastward travel (phase advance), we recommend melatonin timing based on research showing peak effectiveness when taken 3-5 hours before desired bedtime, then transitioning to 30-60 minutes before bed after arrival.
Note: Melatonin is less effective for westward travel (phase delay), where light exposure is the primary tool.
Supporting Research:
- • Burgess et al. (2010) - Preflight adjustment to eastward travel
- • Herxheimer & Petrie (2002) - Melatonin for jet lag (Cochrane Review)
- • Sack (2010) - Clinical practice: Jet lag
Key Research Papers
The following peer-reviewed publications form the scientific foundation of our calculator:
Eastman, C. I., & Burgess, H. J. (2009). How to travel the world without jet lag.
Sleep Medicine Clinics, 4(2), 241-255.
Comprehensive review of jet lag prevention strategies with specific protocols for different travel scenarios.
Burgess, H. J., Crowley, S. J., Gazda, C. J., Fogg, L. F., & Eastman, C. I. (2003). Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light.
Journal of Biological Rhythms, 18(4), 318-328.
Demonstrates effectiveness of pre-flight phase advancing using light exposure.
Khalsa, S. B. S., Jewett, M. E., Cajochen, C., & Czeisler, C. A. (2003). A phase response curve to single bright light pulses in human subjects.
The Journal of Physiology, 549(3), 945-952.
Defines the human PRC to light, essential for calculating optimal light exposure timing.
Herxheimer, A., & Petrie, K. J. (2002). Melatonin for the prevention and treatment of jet lag.
Cochrane Database of Systematic Reviews, (2).
Systematic review showing melatonin's effectiveness for jet lag, particularly eastward travel.
Revell, V. L., & Eastman, C. I. (2005). How to trick mother nature into letting you fly around or stay up all night.
Journal of Biological Rhythms, 20(4), 353-365.
Practical applications of circadian rhythm science for travelers and shift workers.
Scientific Limitations
While our calculator is based on solid research, it's important to understand the limitations:
- Individual variation: Circadian rhythms vary between individuals. Some people are naturally more sensitive to light or adjust faster/slower than average.
- Age effects: Most studies focus on young to middle-aged adults. Older adults and children may respond differently.
- Controlled conditions: Many studies use carefully controlled laboratory settings. Real-world adherence and environmental factors can reduce effectiveness.
- Limited long-haul data: Most research focuses on 6-9 hour time zone changes. Extreme travel (12+ hours) has less data.
- Genetic factors: Chronotype (morning lark vs. night owl) and specific gene variants affect circadian rhythm that we can't measure from simple inputs.
These calculations provide evidence-based guidance, but individual results will vary. The approach is scientifically sound but not a guarantee of perfect results.