Enter your two cities and your flight. Get the real time difference (daylight-saving aware), a jet lag severity score, how many days you'll need to recover — and a concrete plan: when to shift sleep before you fly, when to seek light, when to take melatonin, and when to sleep on the plane.
Pick your cities, departure time, and flight length. Direction (eastward/westward) is detected automatically from the real time-zone math.
Calculate above to generate a plan for your exact trip. General information, not medical advice.
Your personalized pre-flight and post-arrival schedule will appear here.
Should you sleep on the plane? The rule researchers recommend: sleep only when it is nighttime at your destination. We map your flight against the 11 pm–7 am destination window.
Calculate your trip to see your personal sleep window.
Every number below was computed with the same engine that powers the calculator — including daylight-saving quirks.
Verdict: classic red-eye. Sleep on the plane (the whole 7 h flight falls inside London's night), seek morning light on arrival, melatonin at local bedtime.
Verdict: same 5 hours, easier direction — 4 days instead of 5. Stay awake on the plane (it's daytime in New York for the whole flight), seek evening light, delay bedtime.
Verdict: the maximum shift — typical when crossing the international date line. For shifts over 12 h the body adapts via the shorter path — here a 12 h delay. Arriving at 20:00 local is actually ideal: stay up a couple of hours, then sleep at a normal local bedtime.
How the numbers are computed, and the research behind them.
Your body clock runs on roughly a 24-hour cycle driven by the suprachiasmatic nucleus in the brain. Jet lag is the mismatch, in hours, between that clock and local time at your destination. This tool computes the mismatch exactly:
Both offsets are looked up in the full IANA time-zone database built into your browser for the exact instants of takeoff and landing — so daylight-saving transitions, even ones that happen mid-flight, and half-hour zones (India, Nepal) are handled automatically. Nothing is sent anywhere: all of this runs locally on your device.
Flying east requires your clock to advance (shorten the day); flying west requires it to delay (lengthen the day). The human clock finds delaying easier — this eastward vs westward asymmetry is the single biggest factor in how bad jet lag feels. In studies of real travelers the clock shifted about 57 minutes per day after eastward flights and 92 minutes per day after westward flights (Eastman & Burgess, 2009) — rounded here to the planning rates of 1.0 h/day eastward and 1.5 h/day westward (CDC Yellow Book). The severity score multiplies eastward shifts by 1.25 to reflect this asymmetry.
Each day you shift your sleep schedule before departure removes about 0.7 hours from the shift your body must absorb later (Burgess et al., 2003: three days of advanced sleep with morning bright light moved the clock ~2.1 h). These are planning estimates, not clinical predictions — individuals vary.
Bright light is the strongest clock-setting signal. Roughly: morning light advances the clock (use after eastward travel), evening light delays it (use after westward travel) — and wrongly timed light pushes the clock the wrong way. Low-dose melatonin (0.5–3 mg) at local bedtime supports an advance; it is less useful for delays. Your generated plan applies this pattern day by day. This is general information, not medical advice.
This tool estimates circadian jet lag from time-zone math. It does not model age, chronotype, sleep debt, caffeine, alcohol, cabin conditions, or layovers — all of which change real recovery. Treat results as a planning baseline, and see a health professional if sleep problems persist beyond two weeks.
Stack these with your plan above; combined strategies cut recovery time roughly in half versus toughing it out.
Move bedtime ~1 hour per day toward destination time for 2–3 days. Pair with correctly timed bright light.
Eat and sleep on destination time from the moment you board — your brain takes the hint.
Cabin air dehydrates; alcohol fragments sleep. Water is the in-flight drink of choice.
Use it for daytime alertness after arrival, but stop by mid-afternoon local time.
If you must nap on arrival day, keep it to 20–30 minutes, early afternoon — long naps delay adaptation.
Morning outdoor exercise after eastward travel; late-afternoon after westward travel.
Meals are a secondary clock cue. Eat at destination mealtimes from day one, even if you're not hungry.
If you can choose, land in the afternoon or early evening — then sleep at a normal local bedtime.
Straight answers to the questions travelers ask most about jet lag.
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