Jet Lag Calculator: Recovery Days and an Adjustment Plan

How long does jet lag last? Recovery days by time zone

With no plan, jet lag lasts about 1 day for every time zone you cross going east and about 1 day for every 1.5 time zones going west. So 6 hours ahead takes about 6 days, and 8 hours behind also takes about 6. Shifting your sleep for 3 days before you fly takes about a day off.

Those speeds come from real travelers. In their 2009 review, Charmane Eastman and Helen Burgess pulled together field studies and found that the body clock moved about 57 minutes a day after flights east and about 92 minutes a day after flights west. We round those to 1 hour and 1.5 hours a day.

Here's every difference from 1 to 12 hours, worked out by the calculator above, with no preparation:

The east column stops climbing at 10 hours. From there, your body clock gets home faster by going the long way round: shifting later instead of earlier. Eleven hours ahead is the same as 13 hours behind, and 13 hours at 1.5 a day (about 9 days) beats 11 hours at 1 a day. At 12 hours both ways are equally long, so shifting later wins: about 8 days, or about 7 with 3 days of prep.

Small differences matter less. A Lancet review by Jim Waterhouse and colleagues notes that crossing fewer than three time zones is unlikely to cause a big problem; a tired first day is more often travel fatigue.

Jet lag recovery for popular routes from the US

From New York, Western Europe takes about 5 to 6 days to adjust to, the West Coast about 2 days, and Tokyo about 7, because your body treats Tokyo as 10 hours behind, not 14 ahead. Three days of preparation takes about a day off each. The calculator worked out every row for a winter date.

Flying from the US to Asia crosses the date line, so the calendar jumps a day ahead. For your body, though, it's usually a shift later.

Summer time moves some rows. In July, New York to Tokyo is 13 hours ahead on the clock (about 8 days), and New York to Delhi is 9.5 hours ahead, which becomes a shift earlier (about 10 days, 8 with prep). The US and Europe also change clocks on different dates, so for a few weeks a year the Europe rows are an hour off. The Full plan uses your real dates.

Why is jet lag worse when you fly east?

Flying east is harder because your body clock has to move earlier, which means trying to sleep before your body is ready. Flying west asks it to move later, and staying up longer comes easier. The field studies Eastman and Burgess summarized show the gap: about 57 minutes a day going east against about 92 minutes going west.

Here's what that feels like on your first day:

Going to bed at what feels like 5:00 PM is hard. Fly far enough east, though, and the math flips: at 1 hour a day forward and 1.5 back, the long way round is quicker from 9.6 hours ahead. That's why the calculator sometimes moves your sleep later before a flight east.

Your jet lag planner: when to get light and when to avoid it

Bright light moves your body clock, but which way depends on the hour. Light in the hours after your body clock's low point pulls the clock earlier. Light in the hours before it pushes the clock later. So the same morning sun can speed up one trip and slow down another. Your planner times both for you.

This is the method Eastman and Burgess describe: light to shift the clock, with your sleep moving along. The CDC Yellow Book lists timed light as a treatment and suggests a jet lag calculator to time it. Two trips from the tool, for someone who wakes at 7:00 AM, with no prep:

That's why morning sun right after you land in Paris can make jet lag worse: at 8:00 AM your body is still before its low point, so the light pushes it the wrong way. The planner in the tool works this out for every day of your trip, in local time.

How to prepare for jet lag before you fly

Start 3 days before you fly. Going east, go to bed and get up 1 hour earlier each day and get bright light right after you wake. Going west, shift 1 hour later each day and get bright light in the evening. In the calculator, 3 days of preparation takes about a day off most trips.

This is the pre-flight plan Eastman and Burgess recommend for flights east. In a 2005 study by Charmane Eastman and colleagues, 26 young adults spent 3 days moving their sleep earlier with bright morning light, and their body clocks moved earlier too. Shifting 2 hours a day worked no better than 1 hour a day: the body clock couldn't keep up, and falling asleep got harder.

For New York to Paris, with a usual 11:00 PM to 7:00 AM night, the tool gives:

1. 3 days before. Sleep 10:00 PM to 6:00 AM. Bright light 6:00 to 10:00 AM. Last coffee 4:00 PM.
2. 2 days before. Sleep 9:00 PM to 5:00 AM. Bright light 5:00 to 9:00 AM. Last coffee 3:00 PM.
3. 1 day before. Sleep 8:00 PM to 4:00 AM. Bright light 4:00 to 8:00 AM. Last coffee 2:00 PM.

That last alarm is early. If 4:00 AM isn't realistic, do 1 or 2 days: the calculator counts whatever you choose. One exception: from about 10 hours east (New York to Delhi, say), the tool has you go to bed later instead.

We count each prep day as half an hour of real clock shift, a cautious figure: 6 hours at 1 hour a day is 6 days, and 4.5 hours is 5.

On the plane, sleep when it's night where you're going. Leaving New York at 6:00 PM, that's roughly midnight to 7:00 AM Paris time; the planner's flight day shows it for your route.

When to sleep, nap and have coffee after you land

From the first night, sleep at your usual times in local time, even if you feel wide awake. If you need a nap on landing day, keep it to 30 minutes at most and take it before 3:00 PM. Stop caffeine 6 hours before your local bedtime: with an 11:00 PM bedtime, that's 5:00 PM.

The 6 hours come from a sleep study. In 2013, Christopher Drake and colleagues gave 12 healthy sleepers 400 mg of caffeine at bedtime, 3 hours before or 6 hours before. Even at 6 hours, it cut their sleep by more than an hour. The CDC Yellow Book uses the same cutoff: no caffeine in the 6 hours before bed.

The nap limits are our suggestion: short enough not to steal from your first night. For the best length of a nap at home, use the nap calculator.

• Sleep: your normal bedtime and wake-up time, in local time, from night 1. Want a bedtime that fits whole sleep cycles? Try the sleep cycle calculator.
• Coffee: yes in the local morning, none in the 6 hours before bed.
• Meals: eat at local times. It may help you settle into the new day, though the evidence is thin.
• Alcohol: skip the nightcap. The CDC Yellow Book notes that alcohol can help you fall asleep but breaks up your sleep, and that alcohol and caffeine can both dehydrate you, which can make jet lag worse.

Does melatonin help with jet lag?

Probably, if you time it well. A Cochrane review by Andrew Herxheimer and Keith Petrie found that in 8 of 10 trials, melatonin taken close to the target bedtime at the destination (10:00 PM to midnight) eased jet lag after crossing 5 or more time zones. The benefit grew with the time zones crossed and was smaller after flights west.

The CDC Yellow Book lists timed melatonin next to timed light, based on guidance from the American Academy of Sleep Medicine. The key word is timed: melatonin also nudges your body clock, so when you take it matters more than how much. That's why the tool shows timing information only and never a dose.

In the US, melatonin is sold as a supplement, but that doesn't make it right for everyone: the Cochrane authors flag case reports in people with epilepsy and in people taking the blood thinner warfarin.

How we calculate recovery days (and why calculators disagree)

Recovery days are the hours your body clock has to shift, divided by how far it shifts in a day: 1 hour a day earlier, or 1.5 hours later. These speeds round the field data Eastman and Burgess summarized, about 57 and 92 minutes a day. The answer is rounded up and shown as a range, plan to no plan.

The calculator reads the time difference from your real cities and dates, so summer time, half-hour zones like India and the date line are handled. It works out both ways round the clock and picks the faster one, which is why New York to Tokyo counts as 10 hours later, not 14 earlier. Preparation counts as half an hour of real shift per day, at most 3 days. Your body clock's low point sits 3 hours before your usual wake-up time, and the light windows are the 4 waking hours on either side of it.

Other calculators give different numbers because they use different rules of thumb, often without a source:

Tools that only count time zones miss the date line and summer time. Others add age factors with no study behind them; we use none, because the research we checked gives no clear rule to build in. And these are averages: sleep on the plane, the light you get and your chronotype all change your pace. Curious why you bounce back faster than your travel partner? Take the chronotype quiz.

Short trip? When to stay on home time instead

If you're away 3 nights or fewer, we suggest staying on home time instead of switching. Adjusting to Paris takes about 6 days; a 2-night trip ends long before your body gets there, and then you'd have to shift back. The calculator suggests home time automatically for 3 nights or fewer, and you can override it.

Put the meeting or the wedding toast in hours when you'd be awake at home, and keep bright light low around your body clock's low point.

Tick "Plan my trip home too" in the tool to see the trip back, worked out from how far your clock has moved by the day you leave.

Turn your recovery plan into a daily routine

The plan only works if you follow it every day: light at the right time, a coffee cutoff and the same bedtime until your body clock catches up. That's a routine, and a routine sticks best when you run the same steps in the same order each day, at home and away.

One way to do it: put your morning light walk in a Morning Routine in Greatr and your fixed bedtime in an Evening Routine, then run each one in the same order every day. Greatr counts every day you show up, and its app lock can keep the apps that keep you up late locked until you finish your evening routine. When you're home, keep the same two routines to get back into your rhythm. If you want to add more than one habit, habit stacking is the simplest way to chain them.

Your next step: put your flight into the Full plan above, add the planner to your calendar, and set tonight's bedtime to the first one on the list.