Enter your departure and arrival time zones to get your estimated recovery time and a day-by-day plan with light exposure, melatonin timing, and sleep schedule.
Jet lag is not just tiredness from a long flight — it's a genuine physiological disruption of your circadian rhythm caused by rapid crossing of multiple time zones. Your body's internal clock (the suprachiasmatic nucleus in the hypothalamus) regulates not just sleep, but dozens of biological processes — hormone release, body temperature, digestion, immune function, and metabolism — all timed to your home time zone. After rapid transmeridian travel, your body's clock is misaligned with the local environment, producing the constellation of symptoms we recognize as jet lag.
The human circadian clock naturally runs slightly longer than 24 hours — approximately 24.2 hours in most adults. This means the clock naturally tends to drift later (phase delay) rather than earlier (phase advance). Westward travel aligns with this natural tendency — you're extending your day, which the clock does easily. Eastward travel requires phase advance — shortening your day — which the clock resists. This is why New York to London (eastward, 5 hours) typically feels worse than London to New York (westward, 5 hours).
The recovery rate reflects this asymmetry: most people adapt at approximately 1 hour per day for eastward travel and 1.5 hours per day for westward travel. The rule of thumb: expect 1 day of jet lag per time zone eastward, 0.5–0.75 days per time zone westward. A Tokyo-to-New York flight crossing 14 time zones westward may actually recover faster than a shorter eastward journey of similar zone difference.
Light is the primary circadian zeitgeber ("time-giver") — the environmental signal that anchors your internal clock to local time. Strategic light exposure is the most powerful non-pharmacological tool for accelerating jet lag recovery, far more effective than any supplement. The principle: morning light at the destination advances your clock (helping eastward travel); evening light delays your clock (helping westward travel or night-owl tendencies).
For eastward travel: seek bright outdoor light (or a bright light therapy lamp, 10,000 lux) immediately upon waking at the destination, as early as possible. Avoid evening bright light for the first 2–3 days, as your internal body time is still in the afternoon relative to home. For westward travel: seek late-afternoon and evening light at the destination and avoid very early morning bright light.
Light therapy lamps (10,000 lux, used for 20–30 minutes at the right time) are particularly useful for travelers arriving in the morning after overnight flights — the natural light exposure timing may not align with what your clock needs.
Unlike for general insomnia (where evidence is modest), melatonin has strong evidence specifically for jet lag. Taken at the correct time and dose, it shifts the circadian clock by 1–2 hours per night, accelerating adaptation. The correct protocol: take 0.5mg of melatonin at your destination's bedtime for the first 3–4 nights after eastward travel. For westward travel across many zones, take it on the return journey.
The dose matters significantly: 0.5mg is the research-validated effective dose. Most OTC melatonin products contain 5–10mg — 10–20× the effective amount. Higher doses don't shift the clock more effectively and often cause next-day grogginess. Use our Melatonin Calculator for exact dosing and timing guidance.
For significant time zone crossings (5+ hours), pre-travel adaptation can substantially reduce jet lag severity. Starting 3–5 days before eastward travel, shift your bedtime and wake time 30–60 minutes earlier each day. For westward travel, shift later. This partial pre-adaptation means your clock arrives closer to destination time, reducing recovery time. It's impractical for most travelers but valuable for athletes, performers, or executives with critical engagements immediately after arrival.