Jet Lag Calculator

What It Does

Enter your origin and destination time zones and your travel date, your usual bedtime and wake time, the length of the trip and how fast you want to adapt, and the calculator works out the direction of the shift — from the UTC offset each zone carries on that date, daylight saving included — how many days of adjustment it takes and a dated day-by-day schedule of the bedtime and wake time to keep in the destination's local time, with the light to seek on each day. The plan covers every day of the trip and of the stated adjustment, and the adaptation pace is 30, 60 or 90 minutes a day.

Real-World Usage

Jet lag is the mismatch between your body clock and the local day after crossing time zones; it usually lasts about a day per zone crossed and shows up as trouble falling asleep, waking too early, daytime sleepiness and digestive upset. Light is the strongest lever: morning light advances the clock and evening light delays it, which is why the plan tells you which to seek. The plan is also useful before departure — starting the shift two or three days before the flight leaves less to do on arrival — while for trips under three days it is often better to stay on home time.

Local Context

The calculator reads named time zones, not offsets you look up: choose the two zones and the travel date and it works out the UTC offset each one carries on that date — daylight saving included, so a departure from New York on 6 March reads UTC−5 and the same departure on 9 March reads UTC−4. Every clock time in the plan is the destination's local time, dated: a night that runs past midnight shows the following date beside the wake time, and each row names the zone and the offset that row's date carries. The schedule is a plan to keep, not a measurement of your body clock.

World Time Zones at a Glance

Standard UTC offsets, with the summer offset where the region moves its clocks and "no change" where it keeps one all year. Take the offset that applies on your travel dates: southern-hemisphere zones move the other way.

How long does jet lag last?

Roughly one day per time zone crossed, and a little longer going east than going west. A five-hour shift west usually settles within three to five days; the same shift east often takes a day or two more. The plan's adjustment estimate follows the pace you choose — 30, 60 or 90 minutes a day — so at the standard pace a five-hour shift is five days.

Which direction is harder, east or west?

Eastward. The body clock's natural cycle runs slightly longer than 24 hours, so it is easier to delay sleep (westward) than to advance it (eastward). That is why the plan leans on morning light after eastward travel and on evening light after westward travel.

Should I shift before the flight or after I arrive?

Both work. Shifting before departure spreads the change over days when you control your own light and timetable, which suits long trips; once you are there, the destination's daylight does the work. For a trip of two or three days, staying on home time is usually more comfortable than adapting to a clock you will soon leave behind.

Does light matter more than sleep?

It matters more than the timing of any single night. Light entering the eye at the wrong time of day can push the body clock the wrong way: evening light delays it, morning light advances it. Sleeping at the right time supports the change, but light is the signal the clock actually reads.