How long does jet lag last?
Jet lag often lasts several days: the body clock resets by only about 1.5 hours a day after a westward flight, and by barely 1 hour a day eastward (Eastman and Burgess, 2009). After 6 time zones, allow about 4 days going west and 6 days going east.
Simplified diagram. Dotted curves are estimates based on average speeds and the cited studies; everyone resets at their own pace.
How long does jet lag last?
Local time and body time, before and after a 6-time-zone flight. Choose a trip, then tap a label on the drawing to find out what it is.
Sources: resetting speed, temperature low point and light advice (Eastman and Burgess, Sleep Med Clin, 2009); effect of light by time of day (Khalsa, J Physiol, 2003); melatonin (Herxheimer and Petrie, Cochrane, 2002). Drawing not to scale; body clock times after a flight and gap curve: estimates based on average speeds.
Keyboard: 1 to 3 trips, Space pause, L slow motion, R start over, ← → previous or next step.
Frequently asked questions about jet lag
How many days does it take to get over jet lag?
It often takes several days: the body clock resets by about 92 minutes a day after a westward flight and by 57 minutes a day after an eastward one (Eastman and Burgess, 2009). For 6 time zones, as between New York and Paris, that is about 4 days going west and a little over 6 days going east. These are averages: everyone resets at their own pace.
Why is jet lag worse flying east?
Jet lag is worse flying east because the body clock has to move forward, and it does not like moving forward. On average, it runs a little slower than 24 hours: it is much easier to delay it than to advance it (Eastman and Burgess, 2009). Going west, you simply go to bed later, which the body accepts more easily.
How can I avoid jet lag?
You can reduce it by working with light and bedtime. Going east, you need bright light in the morning, but only after the lowest point of body temperature, which comes 3 to 4.5 hours before your usual wake time; before that, the same light delays the clock (Eastman and Burgess, 2009; Khalsa, 2003). Before an eastward flight, shifting your whole schedule earlier by 1 hour a day for a few days, with bright morning light, also helps (Eastman and Burgess, 2009).
When should I take melatonin for jet lag?
Take melatonin in the evening, at local bedtime, between 10 p.m. and midnight. In a review of 10 trials, 9 found that it reduced jet lag after crossing 5 or more time zones, at doses of 0.5 to 5 mg; above 5 mg, there was no added benefit (Herxheimer and Petrie, 2002). Taken too early in the day, it can make you sleepy and slow down the reset. If you have epilepsy or take a blood thinner, ask a doctor first.
Should I sleep on the plane to avoid jet lag?
Yes, when it is night for your body clock; no, when it is daytime for it. What counts is when the body clock sees light and darkness, not the time on your watch (Eastman and Burgess, 2009). In their examples, Eastman and Burgess advise sleeping on the plane when the flight falls at the right time for the body, for example on an overnight eastward flight prepared a few days ahead.
True or false?
Jet lag is the same in both directions.
False. The body clock resets by about 92 minutes a day after flying west, but by only 57 minutes a day after flying east (Eastman and Burgess, 2009).
Melatonin helps with jet lag.
True. Taken at local bedtime, between 10 p.m. and midnight, it reduced jet lag in 9 trials out of 10, after crossing 5 or more time zones (Herxheimer and Petrie, 2002).
To beat jet lag, get as much light as possible as soon as you land.
False. It all depends on the time on your body clock: before the lowest point of body temperature, light delays the clock; after it, light advances it (Khalsa, 2003). After flying east, early morning light can therefore make jet lag worse (Eastman and Burgess, 2009).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
Why is jet lag worse flying east?
Because the body clock moves back more easily than it moves forward: about 1.5 hours a day going west, less than an hour going east. Remaining gap as a percentage of the starting time difference; curves estimated from these average speeds.
| Days after the flight or time of day | Westward, 6 time zones (Paris to New York) (dotted) | Eastward, 6 time zones (New York to Paris) (dotted) | Westward, 9 time zones (Paris to Los Angeles) (dotted) | What happens |
|---|---|---|---|---|
| day 0 | 100 | 100 | 100 | Day 0 after the flight: still 6 h off going west, 6 h going east |
| day 1 | 74 | 84 | 83 | Day 1 after the flight: still 4.5 h off going west, 5.1 h going east |
| day 2 | 49 | 68 | 66 | Day 2 after the flight: still 2.9 h off going west, 4.1 h going east |
| day 3 | 23 | 52 | 49 | Day 3 after the flight: still 1.4 h off going west, 3.2 h going east |
| day 4 | 0 | 37 | 32 | Day 4 after the flight: still 0 h off going west, 2.2 h going east |
| day 5 | 0 | 21 | 15 | Day 5 after the flight: still 0 h off going west, 1.3 h going east |
| day 6 | 0 | 5 | 0 | Day 6 after the flight: still 0 h off going west, 0.3 h going east |
| day 7 | 0 | 0 | 0 | Day 7 after the flight: still 0 h off going west, 0 h going east |
| day 8 | 0 | 0 | 0 | Day 8 after the flight: still 0 h off going west, 0 h going east |
Key points
- Two speeds (Throughout, Shown in humans)
After a flight, the body clock resets by about 92 minutes a day going west, where it has to move back, and by 57 minutes a day going east, where it has to move forward (Eastman and Burgess, 2009). Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - A slightly slow clock (Throughout, Shown in humans)
The human body clock runs on average a little slower than 24 hours: so it is much easier to delay it than to advance it (Eastman and Burgess, 2009). That is why east is harder. Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - About 4 days going west (From day 3 to day 4.2, Hypothesis)
At 92 minutes a day, a 6-hour gap takes about 4 days; 9 hours, about 6 days. These are averages: some people reset faster, others more slowly. Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - About 6 days going east (From day 5 to day 6.5, Shown in humans)
At 57 minutes a day, a 6-hour gap takes a little over 6 days. For a 7-time-zone flight east with no preparation, Eastman and Burgess count 5 days before things are back to normal. Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - Travel fatigue or jet lag? (Until day 1, Shown in humans)
Travel fatigue comes from the flight itself. Jet lag, on the other hand, comes mainly from a body clock that is out of step with local time (Waterhouse, 2007). Source: Waterhouse et al., "Jet lag: trends and coping strategies", Lancet, 2007 - Even for athletes (Throughout, Shown in humans)
In American baseball, teams that had just traveled east lost their next game more often (Recht, 1995); the exact figure is to be checked. Source: Recht, Lew and Schwartz, "Baseball teams beaten by jet lag", Nature, 1995 - Estimated curves (Throughout, Hypothesis)
The curves follow average speeds; in reality, resetting is slower in the first days and everyone has their own pace.
When should you get light to beat jet lag?
Bright light delays the clock if it comes before the lowest point of body temperature, at the end of the night, and advances it if it comes after. Body clock times for someone who sleeps from 11 p.m. to 7 a.m.; curves estimated.
| Days after the flight or time of day | Light that delays the clock (dotted) | Light that advances the clock (dotted) | Body temperature (dotted) |
|---|---|---|---|
| noon | 3 | 0 | 75 |
| 4 p.m. | 6 | 0 | 85 |
| 8 p.m. | 23 | 0 | 87 |
| midnight | 72 | 0 | 47 |
| 4 a.m. | 0 | 21 | 10 |
| 8 a.m. | 0 | 40 | 51 |
| noon | 0 | 5 | 75 |
Key points
- The light response curve (All day, Shown in humans)
In 21 adults, bright light of about 10,000 lux for 6.7 hours delayed the clock when it fell before the temperature low point, advanced it after, and changed nothing right at that moment. Between the largest delay and the largest advance, the gap reached 5.02 hours (Khalsa, 2003). Source: Khalsa et al., "A phase response curve to single bright light pulses in human subjects", J Physiol, 2003 - No dead zone during the day (Until 10 p.m., Shown in humans)
In the same study, daylight kept a small effect: there was no long period when the clock was insensitive to it (Khalsa, 2003). Source: Khalsa et al., "A phase response curve to single bright light pulses in human subjects", J Physiol, 2003 - The low point (From 2 a.m. to 4:30 a.m., Shown in humans)
The lowest point of body temperature usually comes 3 to 4.5 hours before waking, for 8 hours of sleep (Eastman and Burgess, 2009). Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - Going east: morning light (From 4 a.m. to 8 a.m., Shown in humans)
To advance the clock, you need bright light late at night and in the morning, after the low point; the same light taken before the low point delays it (Eastman and Burgess, 2009). Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - Going west: evening light (From 7 p.m. to 2 a.m., Hypothesis)
To delay the clock, evening and early night light helps, as long as it comes before the low point. Source: Khalsa et al., "A phase response curve to single bright light pulses in human subjects", J Physiol, 2003 - Estimated curves (All day, Hypothesis)
The shapes follow Khalsa (2003); the height of the curves is an estimate. After a flight, it is body clock time that counts, not the time on your watch.
When should you take melatonin for jet lag?
In the evening, at local bedtime: taken between 10 p.m. and midnight, local time, it reduces jet lag after 5 or more time zones. Example of a flight from New York to Paris, 6 hours east; curves estimated.
| Days after the flight or time of day | Natural melatonin, before leaving (dotted) | Day 1 in Paris (local time) (dotted) | Day 4 in Paris (dotted) |
|---|---|---|---|
| noon | 2 | 35 | 2 |
| 4 p.m. | 2 | 3 | 2 |
| 8 p.m. | 6 | 2 | 3 |
| midnight | 74 | 2 | 32 |
| 4 a.m. | 85 | 36 | 100 |
| 8 a.m. | 5 | 100 | 40 |
| noon | 2 | 35 | 2 |
Key points
- Melatonin, the night hormone (From 8 p.m. to 3 a.m., Shown in humans)
Melatonin is made by the pineal gland, in the brain, when it is night for the body clock. Its rise starts about 2.5 hours before your usual time of falling asleep (Eastman and Burgess, 2009). Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - 9 trials out of 10 (From 10 p.m. to 12:01 a.m., Shown in humans)
In a Cochrane review of 10 trials, 9 found that melatonin taken close to local bedtime, from 10 p.m. to midnight, reduced jet lag after 5 or more time zones. Treating 2 travelers was enough to help 1 (Herxheimer and Petrie, 2002). Source: Herxheimer and Petrie, "Melatonin for the prevention and treatment of jet lag", Cochrane Database Syst Rev, 2002 - The dose (From 10 p.m. to 12:01 a.m., Shown in humans)
From 0.5 to 5 mg a day, the effect is similar; with 5 mg, people fall asleep faster and sleep better. Above 5 mg, there is no gain (Herxheimer and Petrie, 2002). Source: Herxheimer and Petrie, "Melatonin for the prevention and treatment of jet lag", Cochrane Database Syst Rev, 2002 - The wrong time (Until 6 p.m., Shown in humans)
Taken too early in the day, melatonin makes you sleepy and can delay resetting. Its benefit is smaller going west (Herxheimer and Petrie, 2002). Source: Herxheimer and Petrie, "Melatonin for the prevention and treatment of jet lag", Cochrane Database Syst Rev, 2002 - In the afternoon, to prepare for an eastward flight (From 2 p.m. to 8 p.m., Shown in humans)
Before leaving, small doses taken in the afternoon, several hours before the natural rise of melatonin, advance the clock best (Eastman and Burgess, 2009). Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - A hormone out of step (From midnight, Hypothesis)
On day 1 in Paris, the body still makes its melatonin on New York time: it is high in the morning, when you should be awake. Day after day, the curve moves back toward the night. Source: Eastman and Burgess, "How to travel the world without jet lag", Sleep Med Clin, 2009 - Estimated curves (All day, Hypothesis)
Estimated melatonin profiles, shifted according to the average speeds from Eastman and Burgess (2009).
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