How fast you adjust
The CDC Yellow Book says jet lag appears when you cross at least two time zones, and that the body adjusts at roughly 1 hour per day traveling east and 1.5 hours per day traveling west. Morning light moves sleep and wake times earlier; evening light moves them later.
| Direction | Adjustment | Before the trip | Light |
|---|---|---|---|
| East (e.g. US → Europe) | about 1 h/day | go to bed and get up 1 hour earlier per day | local morning light |
| West (e.g. Europe → US) | about 1.5 h/day | go to bed and get up 1 hour later per day | local evening light |
New York to London
New York is normally five hours behind London. In 2026, the UK leaves summer time on October 25 and the US on November 1, so for that one week the gap is only four hours. If your trip falls around those dates, check the difference for each day. Flying east across five time zones means roughly five days to adjust fully at 1 hour a day, so on a short business trip aim to be alert for your key meetings rather than fully adjusted.
The 2–3 days before
The CDC suggests shifting your sleep by 1 hour a day for 2–3 days before you go: earlier for eastward trips, later for westward ones. Shift only as much as your work allows. Talk to a doctor before using sleep medication or melatonin.
Doing it in the app
Count back from your local wake-up time
Once your phone switches to local time, enter the wake time your plans require in Sleep Calculator’s When to sleep? and you get local bedtimes.
Move it an hour a day before you leave
Before departure, move your wake time an hour a day and recalculate on the same screen. Use Set alarm to put each day’s wake time in your Clock app.
Log your sleep while traveling
Logging your nights in the Log tab shows how much sleep debt the trip cost you. Put the city in the note to find those nights later with search.
FAQ
Can I nap as soon as I land?
If you are exhausted, a short nap (around 20 minutes) and then staying up until local bedtime is a common approach. A long nap pushes night sleep later. See nap lengths compared.
What happens to logged times when I change time zones?
Records are stored exactly as entered. Over a period that mixes time zones, average bed and wake times may not match how it felt.
Sleep Calculator
No sign-up, and your sleep log stays on your phone. Free on Android.