Jet lag calculator
Pick your route and travel date to see how far the clock moves, roughly how long that takes to adjust to, and what your body will think the time is when you land. Free, and no sign-up needed.
Daylight saving changes the answer — Europe and North America switch clocks weeks apart.
Well-known long hauls, both directions
Shift as of today — daylight saving moves some of these by an hour.
| Route | Shift | Rough adjustment |
|---|---|---|
| LHR → JFKLondon to New York | 5 hours behind | 3 days |
| JFK → LHRNew York to London | 5 hours ahead | 5 days |
| LAX → NRTLos Angeles to Tokyo | 16 hours ahead | 16 days |
| NRT → LAXTokyo to Los Angeles | 16 hours behind | 11 days |
| SFO → SINSan Francisco to Singapore | 15 hours ahead | 15 days |
| DXB → LHRDubai to London | 3 hours behind | 2 days |
| SYD → LAXSydney to Los Angeles | 15 hours behind | 10 days |
| FRA → DELFrankfurt to Delhi | 3.5 hours ahead | 4 days |
The same route in the two directions is not the same problem — compare the eastbound and westbound rows.
Common questions
Why is flying east worse than flying west?
The human body clock runs slightly longer than 24 hours left to itself, so stretching a day is easier than cutting one short. Flying west stretches your day; flying east asks you to fall asleep before your body is ready. The usual rule of thumb is about a day of adjustment per time zone going east, and a day per one and a half zones going west.
How long does jet lag last?
As a rough guide, a day per time zone crossed flying east and rather less flying west — so a six-hour eastward shift takes most people the better part of a week to shake off completely. The variation between individuals is wide, and age, sleep quality before the trip, and whether you can get outside on arrival all matter.
Does daylight saving change the shift?
Yes, and it is the reason this calculator asks for a date. Europe and North America change their clocks weeks apart, so London to New York is five hours apart for part of March and six hours for most of the year. A calculator that assumes a fixed offset is wrong precisely during the weeks people are checking it against a real itinerary.
Does light really help?
Light is the strongest signal the body clock responds to. Broadly: after flying east, morning light helps pull your clock forward; after flying west, late afternoon and evening light helps push it back. Getting this backwards can make things worse, which is why the direction matters more than the amount.
Do short flights cause jet lag?
Not if they stay within a time zone, however long they are. A five-hour flight down the same meridian leaves you tired, not jet-lagged, and the two need different remedies. Jet lag is specifically the mismatch between your body clock and the local one.
What this can and can't tell you
The time zone shift is exact. It comes from each airport's IANA time zone, evaluated on the date you give, so daylight saving on either side is accounted for — including the weeks when one continent has changed its clocks and the other has not.
Everything after that is a rule of thumb. The adjustment estimate and the light advice reflect the general pattern — eastward is harder, light early pulls the clock forward, light late pushes it back — but the spread between individuals is far wider than the difference between any two estimates. None of it is medical advice.
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