Jet Lag Calculator guide
Jet Lag Calculator: How Long Jet Lag Lasts and How to Beat It
Our jet lag calculator estimates how long it may take to adjust after crossing time zones, with a simple plan for shifting your sleep and using daylight east or west.
By the AllCalculator editorial teamUpdated 15 October 20265 min read
Long-haul travel is exciting, but jet lag can take the shine off the first days of a holiday or business trip. Tiredness during the day, waking in the middle of the night and feeling generally out of sorts are all signs your body clock hasn't caught up with the local time.
Our Jet Lag Calculator estimates how long you might take to adjust and gives a simple plan for before and after you fly. This guide explains why jet lag happens and practical ways to reduce it.
What is jet lag?
Your body has an internal clock, called your circadian rhythm, which controls when you feel sleepy and alert, as well as hunger, digestion and hormone release. It's set mainly by daylight. When you fly across several time zones quickly, your body clock is still on home time while the clock on the wall says something different.
The NHS describes jet lag as your normal sleep pattern being disturbed after a long flight, and notes that it usually improves within a few days as your body adjusts.
Common symptoms
- difficulty sleeping at night, or waking very early
- tiredness and sleepiness during the day
- poor concentration and memory
- feeling irritable or low
- indigestion, constipation or loss of appetite
How to use the calculator (Jet Lag Calculator)
- Enter the number of time zones you'll cross. London to New York is 5; London to Dubai is 3 or 4 depending on the time of year; London to Sydney is 9 to 11.
- Choose whether you're flying east or west.
- Enter the length of your trip.
The calculator estimates how long you might take to adjust, suggests how to shift your bedtime before you fly, how to use daylight when you arrive, and whether to adapt to local time or stay on UK time for short trips.
A worked example
Flying west from London to New York, crossing 5 time zones, for a week-long trip:
- Likely adjustment: about 3 days
- Before you fly: go to bed about an hour later each night for 3 days
- On arrival: get outside in the afternoon and evening light
- Switch to local meal and sleep times straight away
Try your own journey in the Jet Lag Calculator.
Why flying east is harder
Most people find flying east harder than flying west. Flying east means your day is shortened, so you need to fall asleep earlier than your body wants to. Flying west lengthens your day, and staying up a bit later is usually easier.
A common rule of thumb is that it takes roughly a day per time zone to fully adjust when flying east, and a little less when flying west. Everyone is different, and many people feel mostly normal sooner.
Before you travel
The NHS suggests getting plenty of rest before you travel, and you could start going to bed and getting up earlier or later than usual, closer to the time zone you're travelling to. Even shifting by an hour a day for a few days helps.
Other tips:
- Get a good night's sleep before your flight.
- Plan to arrive in the early evening if you can, so you can go to bed at a normal local time.
- Avoid big meals and too much alcohol before and during the flight.
During the flight
- Set your watch to destination time when you board.
- Sleep on the plane if it's night-time at your destination, using an eye mask and earplugs.
- Drink water regularly. The cabin air is dry. Our water intake calculator explains daily needs.
- Move around and stretch when it's safe to.
After you arrive
The NHS recommends changing your sleep schedule to the new time zone as quickly as possible, going outside during the day because natural light helps your body clock adjust, and not sleeping during the day.
Light: your most powerful tool
Light is the strongest signal to your body clock. After flying east, morning light helps you adjust, while bright light late in the evening can make it harder. After flying west, afternoon and evening light help you stay awake later. Using daylight at the right times can speed up your adjustment.
Medicines and melatonin
Sleeping tablets may help in the short term, and melatonin is sometimes used for jet lag. In the UK, melatonin is a prescription medicine for most adults. Speak to a pharmacist or GP before taking anything, especially if you have other health conditions or take other medicines.
Planning your schedule around jet lag
If you're travelling for an important event, such as a meeting or wedding, try to arrive a day or two early to give yourself time to adjust. Schedule demanding tasks for the times when you're likely to feel most alert, based on your home time zone.
Frequently asked questions
How long does jet lag last?
Usually a few days. Longer journeys and flying east tend to cause more noticeable jet lag.
Does jet lag happen on short flights?
Jet lag is caused by crossing time zones, not flight length. A long flight north to south may cause tiredness but little jet lag.
Do the clocks changing in the UK cause jet lag?
The one-hour change in spring and autumn can feel like very mild jet lag for a day or two.
Should I nap when I arrive?
It's best to avoid daytime sleep. If you must, keep it short, around 20 minutes, and before mid-afternoon.
The Jet Lag Calculator helps you plan for a smoother arrival. If you need to count the days of your trip, our days calculator can help.
Sources and further reading
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This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.