Free Sleep Adjustment Travel calculator with clear step-by-step results.
The body clock shifts roughly one hour a day westward but only about two-thirds of that eastward, because advancing sleep is harder than delaying it. Pre-adapting before departure removes hours from the post-arrival adjustment, and the share-of-trip figure shows whether adapting is even worth attempting.
Effective shift rate
Rate = achievable shift per day / 1.5 when travelling east, unchanged travelling west
Days to adjust
Days = (time zones - hours pre-shifted) / effective rate
General guidance only. Circadian adaptation varies substantially between individuals, and light exposure timing, melatonin and medication all affect it. Seek medical advice for shift work disorder or persistent insomnia.
If adjustment would consume most of the trip, many travellers do better staying on home time for meetings and sleep. Below about three days abroad that is usually the better strategy.
The free-running human circadian period is slightly longer than 24 hours, so delaying sleep comes naturally and advancing it fights the body's own drift.