Sleep calculator / Jet lag calculator
Jet Lag Calculator
See how long it will take to adjust, and get a simple sleep schedule to start before your flight.
- 100% free
- No sign-up
- No app
Why jet lag happens
Your body clock runs on a roughly 24-hour rhythm set mostly by light. When you land in a new time zone, the clock on the wall jumps but your body clock doesn't. For a few days, you're sleepy at the wrong times, awake at 3 AM, and hungry at odd hours until it catches up.
East is harder than west
Most people's natural body clock runs slightly longer than 24 hours, so it's easier to stay up later (flying west) than to fall asleep earlier (flying east). A common rule of thumb is about one day per time zone going east, and a bit faster going west. The calculator uses that estimate.
Shift before you fly
If you can, move your bedtime and wake-up time by an hour a day for up to three days before the trip, earlier if you're flying east and later if you're flying west. You'll arrive partly adjusted.
Use light, the strongest signal you have
- Flying east: get bright morning light at your destination, and keep evenings dim.
- Flying west: get light in the late afternoon and evening, and avoid bright light very early in the morning.
Other things that help
- Switch to destination meal times as soon as you board.
- Go easy on alcohol on the plane. It dehydrates you and fragments sleep.
- If you need to nap after landing, keep it to 20 minutes. The nap calculator can time it.
- Keep caffeine to the morning at your destination. Check your cutoff.
Frequently asked questions
How long does jet lag last?
Roughly a day per time zone crossed going east, and somewhat less going west. A 6-hour eastward trip often takes 4 to 6 days to fully adjust.
Should I sleep on the plane?
Sleep on the plane if it is night-time at your destination. If it is daytime there, try to stay awake, or keep naps short.
Does melatonin help jet lag?
Some research supports melatonin for jet lag, especially flying east. Talk to a pharmacist or doctor about timing and dose, particularly if you take other medications.
Related reading
- Jet Lag From the US to Asia: How to Adjust to Tokyo and Other Big Time ShiftsTokyo is 13 to 17 hours ahead of the US. Here's why that often acts like a westward shift, how long it takes, and a plan for LA or New York.4 min read
- Jet Lag From the US to Europe: A Day-by-Day Plan for New York to London or ParisA concrete plan for New York to London or Paris: what to do 3 days before, on the flight, and each night after you land, with exact times.4 min read
- Why Is Jet Lag Worse Flying East? East vs. West, ExplainedFlying east is harder because your body clock resists running early. Here's why, plus how many days each direction usually takes to recover.4 min read
More free sleep tools
All completely free, no sign-up.
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- Nap CalculatorWhen to set your alarm for a power nap or a full-cycle nap.
- Sleep Debt CalculatorHow much sleep you owe this week, and how to pay it back.
- Caffeine Cutoff CalculatorHow much caffeine is still in you at bedtime, and your latest cup.
- Sleep Needs by AgeRecommended hours for every age, from newborns to over-65s.
- Sleep Efficiency CalculatorWhat share of your time in bed you actually spend asleep.
- Shift Work Sleep CalculatorWhen to sleep and stop caffeine around any shift, including nights.
These results are general estimates, not medical advice. Everyone's sleep is a little different. If you're often exhausted despite enough time in bed, snore loudly, or have been told you stop breathing in your sleep, see a doctor.