What it does
Jet lag happens because your body clock stays on home time after you land. The body clock can only move about an hour a day, so this page spreads the change out: 3 days before you fly, your bedtime and wake-up time move by 1 hour a day, then the rest of the change happens in the first days after you land. Flying east moves your nights earlier; flying west moves them later.
Light is the body clock’s strongest signal, so each day says when to get bright light (daylight or a bright lamp) and when to keep it dim, plus a time for your last coffee or tea. The hour difference is for your flight date, daylight saving included; over 12 hours, it shifts the shorter way round. To size up the bedtimes themselves, use the sleep calculator; to count days to the trip, try date calculator.
How to use it
- Pick the time zones you fly from and to, such as America/Toronto and Europe/London.
- Pick the flight date and your usual bedtime and wake-up time.
- Follow the table: the three days before use home time, the days after use destination time.
What each setting does
- Shift per day: how far sleep moves each day, 30 to 120 minutes. One hour is the usual advice.
- No caffeine for: hours before bed with no coffee, tea, cola or energy drinks. 6 hours is the default.
- Swap directions: plans the trip home.
Worked example
Toronto to London on 20 November 2026: London is 5 hours ahead. With a usual 23:00 to 07:00, bedtimes before the flight are 22:00, 21:00 and 20:00 Toronto time. Three days before, get bright light from 06:00 to 09:00, keep lights dim from 19:00 to 22:00 and have the last caffeine by 16:00. In London, day 1 bed is 00:00 and day 2 is back to 23:00. Flying home the other way, bedtimes move later instead: 00:00, 01:00 and 02:00 London time.
FAQs
What if both places use the same time? The page says no plan is needed.
Why avoid light at some times? Light just after your body’s low point moves the clock earlier; light before it moves it later. Light at the wrong time pushes the wrong way.
Can I take melatonin? Ask a doctor or pharmacist. This page gives no doses.
Where the numbers come from
- Eastman C.I., Burgess H.J. (2009), How to travel the world without jet lag, Sleep Medicine Clinics 4(2): moving sleep about 1 hour a day before the trip, with timed bright light (checked 2026-11-10).
- CDC Yellow Book, Jet lag chapter: flying east is usually harder; morning light helps after flying east, evening light after flying west (checked 2026-11-10).
- Drake C. et al. (2013), Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed, J Clin Sleep Med 9(11): the reason for the 6-hour default, editable.
- Time zone offsets come from your browser's own time zone database (IANA). The plan's light windows are fibub's own simplification.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
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Last updated 2026-11-10.