Jet lag cannot be prevented completely, but you can shorten it and make the first days at your destination far more comfortable. It happens when your internal body clock is out of step with the local time after you cross several time zones. This guide is for anyone taking a long flight who wants a practical plan rather than a list of myths.
The tools that matter most are timing of light, timing of sleep, and what you drink and when. You can start a few days before you fly, but even if you only read this on the plane, there are things you can do on arrival.
What jet lag actually is
Your body runs on a circadian rhythm, an internal clock that cycles roughly every 24 hours and controls sleepiness, body temperature, hunger, and alertness. It is kept in time mainly by light. When you fly across time zones faster than the clock can adjust, you feel sleepy at the wrong hours, wake in the middle of the night, and may have trouble concentrating or an upset stomach.
The US Centers for Disease Control and Prevention (CDC) describes jet lag as a temporary mismatch between the internal clock and local time. The risk factors include how many time zones you cross, the time cues you get at the destination, individual differences, and medication use. The UK's National Health Service (NHS) notes that it usually improves within a few days as the body clock adjusts.
Why east is harder than west
The CDC reports that adaptation averages about 1.5 hours per day after westward travel and about 1 hour per day after eastward travel. The explanation is that the natural rhythm runs slightly longer than 24 hours, so delaying your clock is easier than advancing it.
A rough worked example
Say you fly across eight time zones. Flying east, that is about eight days to fully adjust at 1 hour per day. Flying west, it is about five to six days at 1.5 hours per day. These are averages, not promises. Some people adapt faster, and the number of cues you get from daylight, meals, and activity changes the result.
Plan before you fly
Shifting your schedule before departure gives your body a head start. The CDC suggests shifting your sleep by about an hour per day in the two to three days before travel, later for westward trips and earlier for eastward trips. The NHS gives similar advice: get plenty of rest, and begin moving bedtime and wake time toward the destination's time zone.
You do not have to be exact. Even a gentle shift of 30 to 60 minutes helps. If your work or family life makes shifting hard, concentrate on arriving well rested instead, because starting a long flight already short of sleep makes everything worse.
Use light as your main tool
Light is the strongest signal your body clock responds to, and the timing matters.
- Eastward travel: your clock needs to move earlier. Morning light helps advance it.
- Westward travel: your clock needs to move later. Evening light helps delay it.
- After arrival in general: the CDC advises maximizing natural light at the destination. The NHS recommends spending time outdoors in daylight.
For small shifts of a few hours, these rules work well. For very large shifts, such as eight or more time zones, the timing of light is more complicated, because your body's idea of "morning" may not match the destination's morning for several days. If you cross many zones often, or have a medical condition that affects sleep, ask a doctor or sleep specialist for personalized advice.
Manage sleep, naps, and caffeine
The aim is to sleep when it is night where you are going, and to stay awake when it is day.
- On the plane: If it is night at your destination, try to sleep, and an eye mask and earplugs may help. If it is daytime there, stay awake if you can.
- Naps: The CDC says short naps of 20 to 30 minutes can help you stay alert, while longer naps may disturb night sleep. The NHS advises avoiding daytime sleep after you arrive, so keep any nap short and early.
- Caffeine: Caffeine has a half-life of about five hours, according to the CDC, so a coffee in the afternoon is still partly in your system at bedtime. Use it to get through the morning at your destination, not late in the day.
- Alcohol: Both the CDC and the NHS advise limiting alcohol and caffeine on the flight, since they can dehydrate you and make symptoms worse.
- Water and movement: Drink water, and stretch and walk around the cabin when you can.
What about melatonin?
Melatonin is a hormone your body releases in the evening to signal that it is time to sleep. Supplements are sold in many countries, but guidance differs.
The CDC says that low doses of 0.5 to 1 mg are often enough to shift the body clock, that doses above 5 mg are not recommended, and that timing matters. It also notes that supplement content may differ from the label because the product is not regulated in the same way as medicines in the US. The NHS, by contrast, does not recommend melatonin tablets for jet lag, saying there is not enough evidence that they work.
Rules also vary by country. In some countries melatonin is sold over the counter, and in others it needs a prescription. Because the advice differs and the right use depends on your health and medications, check with a doctor or pharmacist before you try it. Do not combine it with other sleep aids without advice.
A sample plan
This plan is for a trip across about six to eight time zones, flying east. Reverse the direction of the shifts for a westward trip. Adapt it to your situation.
| When | What to do |
|---|---|
| 3 days before | Move bedtime and wake time about an hour earlier. Get morning light. |
| 2 days before | Move another hour earlier. Keep caffeine to the morning. |
| 1 day before | Pack, drink water, and sleep as well as you can. Avoid a late night. |
| Flight | Set your watch to destination time. Sleep when it is night there. Limit alcohol and caffeine. |
| Arrival day | Go outside in daylight. Eat at local mealtimes. Keep any nap under 30 minutes. |
| Days 2 to 4 | Get morning light, keep a fixed wake time, and avoid caffeine late in the day. |
| Days 5 to 8 | Keep to local times. Most of the adjustment should be done. |
Common mistakes
- Sleeping in on the first morning. It feels good, but it delays the adjustment. Set an alarm.
- Napping for hours. A two-hour nap on arrival can make the first night worse.
- Drinking coffee all day to stay awake. It keeps you alert but can ruin sleep that night.
- Trying to adapt on a short trip. For a trip of two to three days, both the NHS and the CDC suggest staying on your home schedule. Plan meetings and meals around your own clock where possible.
- Skipping the plan because it sounds fussy. A little preparation in the three days before you fly is the most reliable step.
Frequently asked questions
How long does jet lag last?
It varies, but a common rule of thumb is about a day per time zone when flying east and a little less going west, based on the adaptation rates above. The NHS says most people feel better within a few days.
Is it better to arrive in the morning or evening?
It depends on your direction and flight time, but the main point is that you should reach your destination's night time rested and ready to go to bed at a local hour. If you land in the morning, stay in daylight and push through until a local evening.
Does exercise help?
Light activity outdoors can help because it combines daylight, movement, and a regular routine. Avoid vigorous exercise close to bedtime if it keeps you awake.
Should I plan for packing and connectivity too?
Yes. A light bag makes the trip less tiring, so see packing light with only a carry-on. You can also set up a phone data plan before you land, as covered in our guide to using your phone abroad.
Next steps
- Work out how many time zones you will cross and whether you are flying east or west, then estimate your adjustment time from the CDC rates above.
- Start shifting your bedtime and wake time by an hour a day, two to three days before departure.
- Plan your light: morning light for eastward trips and evening light for westward trips, and get outdoors on arrival.
- Ask a doctor or pharmacist about melatonin before you decide to use it, especially if you take other medicines.
