Jet Lag Recovery Calculator

1. Enter the time zones and direction. Count the hour difference between home and destination. East means local clocks are ahead of home.
2. Enter your usual wake time. The calculator uses it to estimate your body clock and the best times for light.
3. Add pre-flight days for eastward trips. Shifting your sleep 1 hour earlier a day for 1 to 3 days before you fly gives you a head start.
4. Planning the flight itself? Switch to In-flight sleep window and enter take-off time, flight time and the time difference.

Jet lag happens when you cross time zones faster than your body clock can follow. When you arrive, your sleep-wake cycle is still set to home time, so your body may expect sleep in the middle of the local day or be wide awake at local bedtime. It may begin after crossing at least two time zones, and flying east is usually harder than flying west.

Common symptoms are poor sleep, daytime tiredness, poor concentration and stomach upsets. Jet lag is temporary: it usually improves within a few days as the body clock adjusts. To understand your own clock, try the circadian rhythm calculator.

The calculator divides the shift your clock must make by the average daily shift after flights.

1. Your body temperature low, the sleepiest point of the night, is estimated at 3 hours before your usual wake time, then moved to local time.
2. Going east, light in the 4 hours after that low moves the clock earlier; going west, light in the 4 hours before it moves the clock later.

The AASM rule of one day per time zone is shown as a cross-check.

The NHS advises trying to sleep on the flight if it is night time at your destination. The In-flight sleep window mode turns that into clock times. It converts your take-off time to destination time, treats the 8 hours before your usual wake time as destination night, and marks the part of the flight that falls inside it as your sleep block.

In the awake blocks, drink plenty of water, stretch and walk around the cabin, and go easy on caffeine and alcohol, which the NHS says can make jet lag worse. Examples assume a 7:00 AM wake time. This is general guidance, not medical advice.

Maya usually wakes at 7:00 AM in New York and flies 5 time zones east to London.

Without preparation, Maya’s body low falls at 9:00 AM London time, so early morning light would push her clock the wrong way: she should wear sunglasses on the way in and get outside from mid-morning.

Direction

Going east asks your clock to move earlier, which it does more slowly than moving later.

Number Of Time Zones

More zones means more hours to shift. After 8 or more zones east, the clock often shifts the long way round instead.

Light

Light is the main signal for the body clock; the timing matters as much as the amount.

Caffeine And Alcohol

Caffeine late in the local day delays sleep; check timing with the caffeine and sleep calculator. Alcohol makes sleep more broken.

In a classic example from jet lag research, a 9-zone trip west took about 5 days to adjust, but the return trip east took around 9 to 10 days.

• Crossing 2 or more time zones, when jet lag usually starts to matter.
• Flying east, especially across many zones.
• An important event soon after landing, such as a meeting, exam or race.
• Short trips of 2 to 3 days, where it can be better to stay close to home time than to shift at all.

On arrival, a short early-afternoon nap can bridge the gap without spoiling night sleep; the nap calculator helps time it.

The evidence is mixed, and timing is critical: melatonin at the wrong time can push the body clock the wrong way. The NHS does not recommend melatonin for jet lag because there is not enough evidence that it works, and says sleeping tablets should only be used for a short time if symptoms are severe. Talk to a doctor or pharmacist before taking either.

Getting Morning Light After Flying Far East

If your body low falls after sunrise, early light pushes your clock later. Follow the seek and avoid windows.

Long Naps On Arrival

A long afternoon sleep makes local bedtime harder. Keep naps short and early.

The rates are averages from flight studies; individual travellers vary a lot.

On average about 1 day per time zone after flying east and a little less after flying west, because the body clock shifts about 1.5 hours a day going west.

Going east asks your body clock to move earlier, and it advances more slowly than it delays. You also have to fall asleep before your body is ready.

Get bright light at the right times for your direction, keep to local meal and sleep times, and for eastward trips shift your sleep earlier before you fly.

If you arrive in the morning, stay up until local evening with a short early-afternoon nap at most. Long daytime sleep slows adjustment.

Jet lag may start after crossing two or more time zones, and gets worse with more zones and with eastward travel.

For 2 to 3 days, often not. Keeping close to home hours where possible can be easier than shifting twice.

Usually you are waking because your body is still partly on home time. Getting light at the right times helps it catch up.

If sleep problems last well beyond the expected recovery time or you travel so often that jet lag never settles, talk to a doctor.

• AASM Sleep Education: Jet lag (definition; east harder; about one day per time zone)
• NHS: Jet lag (usually improves in a few days; sleep on the flight if it is night at your destination; melatonin not recommended)
• Eastman and Burgess. How to travel the world without jet lag (Sleep Med Clin, 2009) (1 h/day east, 1.5 h/day west; light timing around Tmin; wrong-direction shifts)
• Burgess et al. Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light (J Biol Rhythms, 2003) (2.1 h advance with bright light vs 0.6 h dim)