Jet Lag Time Shift Calculator
Estimate the time zone shift for a trip and a rough number of days your body clock may take to adjust.
Your results
This is a general rule-of-thumb estimate, not a medical prediction. Individual recovery varies widely.
Calculation breakdown
- Eastward estimate
- Time zones crossed × 1 day
- Westward estimate
- Time zones crossed × ~0.67 day
Worked example
Flying from Sydney to London crosses roughly 10-11 time zones (varies with daylight saving); eastward-style rules suggest around 8-10 days for full adjustment.
Assumptions
- General estimates only, not medical advice.
- Individual adjustment depends on sleep, light exposure, age and overall health.
How this calculator works
This calculator works out the number of time zones you're crossing and gives a general estimate of adjustment time, commonly cited as roughly one day per time zone crossed eastward and slightly less westward. Use it as a rough planning guide, not a medical prediction.
Frequently asked questions
Why does direction of travel matter?
Most people find it harder to adjust travelling east (losing time) than west (gaining time), so eastward trips are often given a slightly longer adjustment estimate.
Is this medically accurate?
No, it's a general rule-of-thumb estimate. Individual jet lag recovery varies with sleep, light exposure, age and health.
Does a short flight with a big time zone change cause more jet lag than a long flight with little change?
Generally yes, jet lag is driven mainly by the number of time zones crossed, not the length of the flight itself.
Results are estimates only and are not financial, tax, legal or credit advice.