Jet Lag Calculator
Estimate jet lag recovery from time zones crossed.
Returns adjustment days, circadian shift, and sleep schedule tips for eastward and westward travel.
Jet lag severity is driven by the number of time zones crossed, travel direction, and the individual’s circadian sensitivity. The standard estimation formula is:
Recovery Days = Time Zones Crossed × Direction Factor / Adaptation Rate
Where:
- Direction Factor: Eastward travel = 1.5 (harder — shortens the day, requires phase advance); Westward = 1.0 (easier — extends the day, phase delay)
- Adaptation Rate: The circadian clock shifts approximately 1–1.5 hours per day naturally
So the simplified rule is:
Recovery Days (East) ≈ Time Zones × 1.5 / 1.0 Recovery Days (West) ≈ Time Zones × 1.0 / 1.0
Worked Example — New York to London (5 time zones east):
- Recovery = 5 × 1.5 = 7.5 days for full circadian realignment
- Rule of thumb: 1 day per zone east, so expect 5 days until feeling normal
- Practical impact: first 2–3 days have the worst fatigue
London to New York (westward, 5 zones):
- Recovery = 5 × 1.0 = 5 days
Mitigation Strategies and Their Efficacy:
- Light exposure at destination time: accelerates adjustment by 1–2 days
- Melatonin (0.5–5 mg at local bedtime): reduces symptoms by ~50% in studies
- Staying hydrated (cabin humidity is ~12%, vs comfort level of 40–60%)
- Pre-flight schedule shift: sleeping 1 hr earlier/later for 3 days before departure
Worst-case route: Los Angeles to Singapore crosses 15+ time zones and may cause symptoms for 10–14 days without mitigation.