Jet Lag Planner

Your body clock moves about 1 hour a day after flying east and about 1.5 hours a day after flying west, so New York to Paris (6 hours ahead) takes about 6 days, and Los Angeles to Tokyo (8 hours behind, folded round the clock) about 6. Daylight at the right time speeds it up.

How to use it

Type where you fly from and to, pick the day you land (daylight saving changes the difference), and set when you usually go to bed and wake up. Add the nights you stay if it is a short trip. The answer is the number of days your body clock needs, the first day it should get easier, and a table: each day, where your body’s low point falls in local time, when to get daylight and when to avoid bright light.

The rule, and where it comes from

The planner runs on the model in Eastman and Burgess’s How To Travel the World Without Jet lag (Sleep Medicine Clinics, 2009), from the Rush University sleep laboratory. “Flying east requires a phase advance of the circadian clock, and flying west requires a phase delay.” After landing, their worked example’s clock moves west at 1.5 hours a day (“The Tmin phase delays by 1.5 h/day after landing in Beijing”) and east at 1 hour a day (“his circadian clock may phase advance by 1 h/day”). “As mentioned above, it is easier for most people to phase delay than to phase advance.” The clock’s marker is the body temperature minimum, the Tmin, the sleepiest time of the night: “Under usual circumstances, the Tmin occurs about 3 to 4.5 h before wake time with an 8 h sleep episode.” The planner puts it 3 hours before your wake time, as their example does.

Light is the lever: “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.” So after flying east, get daylight after your low point and avoid it before; after flying west, the reverse. The NHS says the simple version: “go outside during the day – natural light will help your body clock adjust”.

How long jet lag lasts, route by route

Days until your body clock is fully on local time, landing on October 10, 2026, sleeping 11 p.m. to 7 a.m.:

Tokyo is 16 hours ahead of Los Angeles on the clock, but your body only knows the hour of the day: 16 ahead is 8 behind, and delaying 8 hours is the shorter way. Going east across 8 or more zones, the clock can go either way; the source puts it as a guideline, “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”, and the light timing in the table is what keeps it moving the way you want.

Worked examples

New York City to Paris, landing October 10. Paris is 6 hours ahead. Your low point, 4 a.m. at home, is 10 a.m. in Paris on landing day, so avoid bright light before 10 a.m. and get outside after it. It moves an hour earlier each day: 7 a.m. on day 3, 6 a.m. on day 4, inside your night’s sleep, and 4 a.m. on day 6.

Los Angeles to Tokyo. 8 hours behind, folded round the clock. Your low point lands at 8 p.m. Tokyo time: get daylight before it, avoid bright light after it. At 1.5 hours a day it is 11 p.m. on day 2, already inside your sleep, and back at 4 a.m. on day 6.

A weekend in London. Two nights: CDC’s advice is to stay on home time. “If a traveler spends ≤2 days in the new time zone, they might prefer to anchor their sleep–wake schedule to the time of day at home as much as possible.”

Common mistakes

• Morning sun after flying east from the U.S. On landing day in Europe your body’s low point is mid-morning; bright light before it pushes your clock the wrong way. Sunglasses until then, then outside.
• Counting the hours on the clock, not round it. A 16-hour difference is an 8-hour shift for your body.
• Calling every tired day jet lag. “For travelers crossing ≤3 time zones, especially if they are on a long-haul flight, symptoms (e.g., tiredness) are likely due to fatigue rather than jet lag, and symptoms should abate 1–3 days post-flight.”
• A drink to sleep. “Travelers should not use alcohol as a sleep aid, because it disrupts sleep and can provoke obstructive sleep apnea.”
• Taking melatonin without asking. The sources disagree: “The American Academy of Sleep Medicine and the US National Center for Complementary and Integrative Health suggest that melatonin could be used to reduce symptoms of jet lag, although they caution that melatonin might not be safe when combined with some other medications.” The NHS: “Melatonin tablets are not recommended on the NHS for jet lag because there’s not enough evidence to show they work.” Ask your doctor.

Plan the trip

For the flight itself, read the Long Flight Survival Guide and how to arrive functional after a red-eye flight. Flying to Paris? See which U.S. cities fly there direct. Then check the flight time and arrival time, when to leave for the airport and a packing list.