Jet Lag Calculator
Estimate baseline days to adapt to time zones crossed, using average eastward and westward rates.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
This baseline estimate uses CDC Yellow Book average adaptation rates: about 1 time-zone hour per day eastward and 1.5 hours per day westward. Individual adjustment varies with light timing, sleep, itinerary and health; the this is not a medical rating or personalized treatment plan.
Worked example
calculated with the default values below
Time zones crossed 6 · Direction of travel Eastward (advancing the clock) · Night flight Day flight Baseline adaptation estimate 6.0 days · Planning prompt Eastward travel shifts the body clock earlier; review destination-time light and sleep guidance · Note Adaptation varies; use destination-time cues and current travel-health guidance
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
D = Δz ÷ r_d
- D
- baseline adaptation estimate (days)
- Δz
- time-zone hours crossed
- r_d
- average adaptation rate: east 1 h/day; west 1.5 h/day
Uses CDC Yellow Book average rates: eastward 1 time-zone hour/day and westward 1.5 hours/day. This is a baseline estimate, not an individual forecast or clinical assessment.
Frequently asked questions
How are baseline adjustment days estimated?
The estimate divides time zones crossed by CDC Yellow Book averages: about 1 hour per day eastward or 1.5 hours per day westward. Individual adjustment varies; this is not a personal forecast or medical assessment.