Jet lag happens when fast travel across time zones desynchronizes your internal circadian clock from the local day-night cycle, leading to fatigue, poor sleep, and reduced concentration.

How long does jet lag last?

As a rule of thumb your circadian rhythm shifts roughly one hour per day, so a six-hour time change typically takes several days to fully adjust. Eastward travel is usually harder than westward.

Can a planner actually reduce jet lag?

Yes. A structured plan that times sleep, light exposure, and activity in the days before and after a flight can meaningfully shorten adjustment compared with doing nothing.

Is Jet Zzz free to use?

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Jet Lag from Chicago to London: How Long & How to Beat It

Jet Lag from Chicago to LondonLondon runs 6 hours ahead of Chicago — a eastbound shift over a roughly 8-hour flight. Expect about 6 days to feel close to normal in London.What to expectEastward shifts compress the day and fight the natural drift of the human circadian rhythm, so they tend to feel harder than westward shifts of the same magnitude.Adjustment playbook

Shift bedtime earlier by ~1 hour per day before departure.

Reset your watch to London time at boarding.

On arrival, get bright morning light and avoid bright evening light.

Caffeine in the morning only.

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