Jet Lag Calculator
See how long jet lag will last on your route — and get a personalised plan to beat it, with a pre-flight sleep schedule and light-timing advice.
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London is 5 hours ahead of New York — a noticeable shift in the eastward direction. Eastward trips are usually the harder direction, because your body finds it easier to stay up later than to fall asleep earlier. Plan for roughly 5 days to feel fully adjusted, and you can take the edge off by starting before you leave.
Shift your clock before you fly (go to bed earlier)
| Night before you fly | Lights out 7:00 PM |
| 2 nights before | Lights out 8:00 PM |
| 3 nights before | Lights out 9:00 PM |
| 4 nights before | Lights out 10:00 PM |
Move your bedtime about an hour a day toward London time. Even a partial shift shortens the adjustment.
Light is your fastest reset
Heading east, you need to wake your body clock earlier. Seek bright light in the morning at London, and dim the lights and avoid screens in the late evening.
General guidance, not medical advice. Melatonin and light timing affect people differently — check with a doctor before using melatonin, especially if you are pregnant, taking medication, or managing a health condition.
How long does jet lag last, and how do I beat it fast?
Plan for about one day of recovery per time zone crossed flying east, and roughly one day per 1.5 zones flying west — so a typical 5 to 8 hour shift takes 4 to 8 days to fully clear. You can cut that down by shifting your sleep schedule about an hour a day before you leave, then using well-timed daylight at your destination: morning light for eastward trips, evening light for westward ones.
Methodology: Recovery uses the widely cited rule of about one day per time zone eastward and one day per 1.5 zones westward, with eastward (phase-advance) trips treated as the harder direction. Time-zone offsets — including daylight saving for your travel date — are computed live in your browser. Light and melatonin guidance follows mainstream circadian and travel-medicine advice; it is general information, not medical advice. How we test & calculate.
What Is a Jet Lag Calculator?
A jet lag calculator turns your route into the two things you actually need: how long the jet lag is likely to last, and what to do about it. It looks at how many time zones you are crossing and in which direction, then estimates your recovery time and builds a simple plan — when to shift your bedtime before the flight, and when to seek or avoid light once you land. Instead of guessing how rough the first few days will be, you get a realistic estimate in seconds.
It is built for the planning stage: deciding when to fly, how many buffer days to leave before an important meeting or event, and how early to start preparing at home. The harder the shift, the more a little preparation pays off.
How Long Does Jet Lag Last?
The most widely used guide is about one day of adjustment per time zone when you fly east, and roughly one day per one-and-a-half time zones when you fly west. A five-hour eastward shift, then, might take around five days to clear fully; the same trip in the other direction often settles in three to four. The worst of it usually lands in the first two or three days, easing steadily after that. These are averages — your own pace depends on sleep, light, age, and how much you prepared.
Why Eastward Travel Is Harder
Left to its own devices, the human body clock runs a little longer than twenty-four hours. That makes it easy to stretch a day — to stay up later and wake later — but harder to compress one. Flying west asks you to delay your clock, which your body does happily. Flying east asks you to advance it, fighting your natural drift. That single fact is why eastward jet lag tends to be worse, and why the calculator weights the two directions differently.
How to Beat Jet Lag
The levers that actually move the needle, in rough order of impact:
- Shift before you fly: move your bedtime about an hour a day toward your destination for a few days beforehand — earlier for eastward trips, later for westward ones.
- Use light deliberately: light is the strongest reset there is. Heading east, seek morning light and avoid it late in the evening. Heading west, seek evening light and avoid bright early mornings at first.
- Set your watch on boarding: switch to destination time the moment you sit down, and decide whether to sleep based on the local clock you will land on.
- Be smart about naps: a short twenty-to-thirty-minute nap helps; a long late-afternoon sleep locks the jet lag in.
- Consider melatonin: a low evening dose at the destination can help on eastward trips — check with a doctor or pharmacist first.
- Hydrate and ease off alcohol: both make the first days harder than they need to be.
🧮 Plan the rest of your trip
Light Timing, the Short Version
The reason timing matters is that the same bright light can shift your clock in opposite directions depending on when you get it. In the hours after your natural low point — early morning for most people — light pulls your clock earlier, which is what you want flying east. In the hours before it — the evening — light pushes your clock later, which is what you want flying west. Getting the timing backwards can actually slow you down, so the calculator spells out which side of the day to favour for your specific direction of travel.
Jet Lag vs Travel Fatigue
They feel similar on arrival but are not the same thing. Travel fatigue is the all-over tiredness of a long journey — dehydration, cramped seats, odd meal times — and it clears with one solid night of sleep, whichever way you flew. Jet lag is specifically the mismatch between your body clock and the local clock after crossing time zones, and it only fades as your internal rhythm catches up. A long north-south flight can leave you exhausted yet cause no jet lag at all, because you never changed time zones.
Who Gets Jet Lag Worst
Anyone crossing three or more time zones can feel it, but the experience varies. Larger shifts and eastward trips are reliably harder. Individual factors — sleep quality, age, flexibility of schedule, and how much daylight you get in the first days — all shape how quickly you bounce back. The plan above works for everyone; the difference is mostly in how many days to budget, which is exactly what the calculator estimates for your route.
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Frequently Asked Questions
How long does jet lag last?
A useful rule of thumb is about one day of adjustment per time zone crossed when flying east, and roughly one day per 1.5 time zones when flying west. So a 6-hour eastward shift might take around 6 days to fully clear, while the same trip westbound often settles in 4 days or so. Most people feel the worst of it in the first two or three days, then improve steadily. The calculator above applies this model to your specific route.
Why is flying east worse than flying west?
The human body clock runs slightly longer than 24 hours, so it is naturally easier to stay up later (delay) than to fall asleep earlier (advance). Flying west asks you to delay your clock, which your body does willingly. Flying east asks you to advance it, working against your natural drift — which is why eastward jet lag tends to hit harder and last longer.
How many time zones cause jet lag?
Jet lag generally starts to be noticeable after crossing about three or more time zones. One or two zones usually produce only mild, short-lived effects. The more zones you cross, the longer the adjustment — though above roughly 12 zones the shift effectively wraps around, and your body may adapt the "short way" in the opposite direction.
How can I prevent or reduce jet lag before I fly?
Start shifting your sleep schedule toward your destination a few days before departure — about an hour a day. Fly well rested rather than sleep-deprived, set your watch to destination time when you board, and decide whether to sleep on the plane based on the local time you will land. Even a partial pre-trip shift noticeably shortens how long it takes to feel normal at the other end.
Does light exposure really help with jet lag?
Yes — light is the single most powerful tool for resetting your body clock. Timing matters: heading east, seek bright morning light and avoid light late in the evening to pull your clock earlier. Heading west, seek light in the late afternoon and evening and avoid bright early-morning light to push your clock later. Getting outside into daylight at the right time of day does more than almost anything else.
Does melatonin work for jet lag?
Low-dose melatonin taken in the evening at your destination can help advance your clock on eastward trips, and several travel-medicine bodies consider it a reasonable option. Timing and dose matter, and it is not right for everyone. Treat the calculator guidance as general information and check with a doctor or pharmacist before using melatonin, particularly if you are pregnant, taking other medication, or managing a health condition.
How accurate is the recovery estimate?
It is a planning estimate, not a medical prediction. The day-per-time-zone model is a widely used average, but real recovery varies with age, sleep quality, how much light you get, whether you pre-adjusted, and individual differences. Use the figure to plan buffer days and important meetings, then expect your own pace to vary by a day or two either way.
Should I nap when I arrive?
Short naps of 20 to 30 minutes can take the edge off without wrecking that night sleep. Long naps, especially in the late afternoon, tend to lock in the jet lag by keeping your clock on the old schedule. The faster route to recovery is usually to stay awake until a normal local bedtime, helped along by daylight and activity.
Does jet lag affect children and older travellers differently?
It can. Young children often adjust quickly but on their own unpredictable schedule, so building in flexible days helps. Older travellers sometimes find adjustment slower and the effects more pronounced. For everyone, the same levers apply — light timing, a gradual schedule shift, hydration, and patience over the first few days.
Is jet lag the same as travel fatigue?
No. Travel fatigue is the general tiredness from a long journey — dehydration, cramped seats, disrupted meals — and it clears with a good night sleep regardless of direction. Jet lag is specifically the mismatch between your body clock and local time after crossing time zones, and it only resolves as your internal clock re-synchronises. A north-south flight can leave you fatigued but cause no jet lag at all.