Jet lag happens when your body clock, which governs when you feel sleepy, hungry and alert, is out of step with the time where you are. Fly from London to San Francisco and your body thinks it is evening when the city is having lunch. Fly from Boston to San Francisco and you will wake at dawn for no obvious reason. The body clock does adjust, but slowly; a common rule of thumb is about a day for each time zone crossed. With a few deliberate steps, you can speed that up and make the first days of a short trip far more enjoyable.
Know which way you are going
Direction matters. Flying west, as most travelers from Europe to San Francisco or Boston do, makes the day longer, and most people find it easier: you stay up a little late and then sleep well. Flying east shortens the day and asks your body to fall asleep before it is ready, which is usually harder. San Francisco is three hours behind Boston, and Western Europe is roughly five to six hours ahead of Boston and eight to nine hours ahead of San Francisco. Those numbers tell you how much adjusting you will have to do.
Before you fly
- Shift gradually. In the few days before departure, move your bedtime and wake time an hour or so toward the destination's schedule. For a westward trip, go to bed and get up later; for an eastward one, earlier.
- Arrive rested. Starting a long trip already short of sleep makes everything worse. Pack the day before, not the night of.
- Choose flights carefully where you can. An arrival in the afternoon or early evening often works well, because you only need to stay awake for a few hours before a normal bedtime.
On the plane
- Switch to destination time as soon as you board. Set your watch and phone and start thinking in local time.
- Sleep if it is night where you are going, and try to stay awake if it is day. An eye mask, earplugs and a neck pillow help.
- Drink plenty of water. Cabin air is dry, and dehydration adds to the fatigue.
- Go easy on alcohol and caffeine. Both disrupt sleep, even when a drink seems to make you drowsy.
- Move around. Walk the aisle and stretch when it is safe to do so.
On arrival: use daylight
Light is the strongest signal your body clock receives, so timing your exposure to it is the most effective tool you have. As a general guide, after a westward flight, get bright outdoor light in the late afternoon and early evening to help you stay up later. After an eastward flight, get morning light, and avoid bright light late in the evening. Even on an overcast or foggy day, outdoor light is far stronger than indoor lighting.
In practice, that means getting outside rather than collapsing in the hotel room. A gentle walk along San Francisco's Embarcadero, through Boston Common or across the Public Garden is ideal: fresh air, light and movement, with nothing demanding.
The first day and night
- Eat at local mealtimes, even if you are not very hungry. Meals help set your body clock.
- Nap briefly or not at all. If you must sleep in the afternoon, keep it short and set an alarm. A long nap can leave you wide awake at night.
- Stop caffeine by early afternoon so it does not keep you up.
- Go to bed at a normal local time, or close to it.
- Keep the room dark and cool. If you wake early, which is common after flying west, keep the lights low and rest rather than reaching for your phone.
Some people take sleep aids or supplements for jet lag. Speak to a doctor or pharmacist before trying anything, especially if you take other medication.
Plan a gentle start
Do not put your most important or most demanding activity on day one. Save booked tours and long hikes for the second or third day, and keep the first day flexible and outdoors. Our itineraries for San Francisco in three days and Boston in two days both work well if you shuffle the lighter days to the front. If you are arriving from overseas, our guide to entering the US covers what to expect before you reach the city.
Frequently asked questions
Is jet lag worse going east or west?
For most people, flying east is harder, because it is more difficult to fall asleep early than to stay up late.
Should I stay awake all day after an overnight flight?
Try to stay up until a reasonable local bedtime, with at most a short nap. A long sleep in the middle of the day tends to prolong jet lag.
Is it worth adjusting for a very short trip?
For a trip of only a day or two, some travelers stay close to their home schedule instead. For anything longer, adjusting quickly pays off.