Free tool
Jet Lag Planner
Plan when to sleep, when to seek daylight and when to avoid it, from a few days before you fly to your first days at the destination. Based on published guidance on how light shifts the body clock, with a calendar download for the trip.
Your adjustment
Setting example times…
How the plan works
- Time difference. The planner compares the two clocks at your arrival time, including daylight saving time in either place. Across the International Date Line it uses the time of day, not the date: Los Angeles to Sydney is 19 hours ahead on the clock, which your body treats as 5 hours behind.
- Direction. If the destination is ahead, your body clock needs to move earlier (advance); if it is behind, later (delay). From 8 hours east, the plan delays the long way round by default, because the clock often shifts that way anyway. You can change this.
- Before you fly. Bedtime and wake time move 1 hour a day in the right direction, for as many days as you choose (the CDC suggests 2–3).
- After you land. You sleep at local night-time from the first night. Your body clock is assumed to catch up at about1 hour a day when advancing and 1.5 hours a day when delaying, the average rates the CDC gives.
- Light. Each day the planner estimates your body clock’s low point (the core body temperature minimum), which usually falls 2–4.5 hours before your natural wake time; it uses3 hours. Light in the hours after the low point moves the clock earlier, and light in the hours before it moves the clock later. Light has most effect within 3–6 hours of the low point; the plan uses windows of up to 6 hours and shows only the parts that fall while you are awake.
- Caffeine (optional). A cut-off 6 hours before each night’s bedtime, as sleep research and the CDC suggest, so it does not disturb the sleep you are trying to move.
Limits of the plan
These are averages from research and official guidance, and people vary. The plan does not know your flight’s cabin lighting, whether you can sleep on board or how much daylight there is at the destination. Treat the windows as a guide, keep to local meal and sleep times, and avoid long daytime naps, as the NHS advises.
Not medical advice
This planner is general guidance about light and sleep timing, not medical advice. It does not recommend any medicine. If you are thinking about melatonin, sleeping tablets or anything else, or you have a health condition, are pregnant or take regular medication, speak to a doctor or pharmacist first. The NHS does not recommend melatonin for jet lag, and in the UK it is available on prescription only.
Questions & answers
How long does jet lag last?
Without any special measures, the body clock typically adjusts by about 1.5 hours a day after flying west and about 1 hour a day after flying east, according to the CDC. Crossing eight time zones east can take a week or more, while three zones west may take two days. Shifting your sleep for a few days before you fly, and timing your light exposure, can shorten this.
Why is flying east worse than flying west?
Flying west asks the body clock to move later, and flying east asks it to move earlier. The clock finds moving later easier: the CDC gives average rates of about 1.5 hours a day westward against 1 hour a day eastward. After an eastward flight you are also trying to sleep and wake at what your body still treats as the middle of the night.
When should I seek or avoid light after flying east?
Light just after your body clock’s low point (roughly 2–4.5 hours before your usual wake time) moves the clock earlier; light just before it moves the clock later. After a moderate eastward flight, that low point falls in the destination morning, so very early light can work against you and late-morning light helps. The planner works out these windows for each day and moves them as you adjust.
What about long trips east, such as London to Tokyo?
For 8 or more time zones east, the body clock often shifts the other way, later rather than earlier. Some researchers therefore suggest deliberately delaying the clock on these trips; others still advance it. The planner delays from 8 hours east by default and lets you switch.
Should I take melatonin for jet lag?
The NHS says melatonin tablets are not recommended on the NHS for jet lag because there is not enough evidence that they work, and that medicines are not usually needed. In the UK melatonin is prescription-only. The CDC notes that its timing matters and taking it at the wrong time can make things worse. This planner does not advise on melatonin or any medicine: speak to a doctor or pharmacist.
Can I use this to plan a client’s trip?
Yes. Set the home time zone to your client’s, enter the flight times from the itinerary and their usual sleep pattern, then copy the plan as text or send the calendar file with their travel documents. Nothing is stored: the plan is created in the browser and the share link holds only the inputs.
Sources & data
Every figure this tool uses by default is listed here with where it came from and when we last checked it. Spotted something out of date? Tell us.
- Typical body-clock adjustment per day after a flight (eastward advance / westward delay)CDC Yellow Book 2026: “westward travel is easier to adapt to than eastward travel, with an average rate of adaptation of 1.5 hrs/day for westward travel and 1 hr/day for eastward travel.” Eastman & Burgess (2009) cite early estimates from real travellers of 92 min/day (phase delays, westward) and 57 min/day (phase advances, eastward). Averages: individuals vary.
- Recommended pre-flight shift of the sleep schedule per dayCDC Yellow Book 2026: “shifting sleep 1 hour later (for westward travel) or earlier (for eastward travel) per day in the 2–3 days prior to the trip may reduce the amount of time required to adjust”. Eastman & Burgess (2009): “we do not recommend advancing the sleep schedule more than 1 h/day”; with a light box they estimate delays of up to 2 h/day are achievable, so 1 h/day is the conservative figure for both directions.
- Suggested number of days to shift sleep before departureCDC Yellow Book 2026: “in the 2–3 days prior to the trip”. Eastman & Burgess (2009) use 2–4 days in their worked examples and note that “even just one or two days of a preflight shift will help reduce the subsequent jet lag.”
- Body-clock low point (core body temperature minimum) before usual wake timeEastman & Burgess (2009): “Under usual circumstances, the Tmin occurs about 3 to 4.5 h before wake time with an 8 h sleep episode”, and use 3 h before wake in their worked example. CDC Yellow Book 2026 places the “circadian nadir (approximately 2–4 hours prior to habitual wake time)”. The sources differ slightly and it varies between people; the planner uses 3 hours (TMIN_MODEL_HOURS_BEFORE_WAKE), which sits inside both ranges.
- Light timing rule (phase response curve): light after the body-clock low point advances it, light before delays itEastman & Burgess (2009): bright light “can help produce phase advances when applied late in the sleep episode and in the morning after the Tmin, and can help produce phase delays when applied early in the sleep episode before the Tmin”; the crossover is “around the time of the Tmin or a little later”. CDC Yellow Book 2026: morning light after the circadian nadir “promotes phase advances”, evening light “generally promotes phase delays”.
- Window either side of the body-clock low point where light has the largest effectRoach & Sargent (2019): “the largest shifts occur when light exposure occurs in the 3–6 h either side of CBTmin.” A single review; the planner uses 6 hours (LIGHT_WINDOW_MODEL_HOURS) and then shows only the part of each window that falls in waking hours.
- Eastward time difference from which delaying the body clock is suggested instead of advancing itEastman & Burgess (2009): “Antidromic re-entrainment is common following eastward travel, especially when 8 or more time zones are crossed”, and suggest to “phase advance the circadian clock for crossing up to 7 time zones east and phase delay the clock for crossing 8 or more time zone east”, adding this “may not always apply to all individual travelers.” Roach & Sargent (2019) instead advance for an 8-hour eastward example (Los Angeles to London). The sources differ at the boundary, so the planner lets you choose the direction.
- Stop caffeine this long before bedtimeDrake et al. (2013): 400 mg of caffeine even 6 hours before bed reduced total sleep, supporting “sleep hygiene recommendations to refrain from substantial caffeine use for a minimum of 6 hours prior to bedtime.” A small study (12 healthy sleepers) at a high dose. The CDC Yellow Book 2026 example plan also says to stop caffeine 6 hours before bedtime and gives caffeine’s half-life as about 5 hours.
- Official position on melatonin for jet lag (NHS and CDC)NHS: “Melatonin tablets are not recommended on the NHS for jet lag because there’s not enough evidence to show they work” and “Medicines are not usually needed for jet lag.” CDC Yellow Book 2026: “It is important to appropriately plan melatonin as taking it at the wrong time can increase misalignment”, and notes melatonin is not regulated by the US Food and Drug Administration. In the UK melatonin is prescription-only. This tool gives no melatonin timing or dosing advice.
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