Jet lag recovery time depends primarily on the number of time zones you cross. As a general rule, your body needs roughly one day per time zone to fully re-synchronise its circadian rhythm — so crossing 6 time zones can mean up to 6 days of disrupted sleep, digestion, and alertness. Eastward travel tends to extend that window because it forces your body to advance its clock, which is harder for most people than delaying it. Other factors that affect how long jet lag lasts include your age (older travellers often recover more slowly), overall sleep quality before the trip, hydration during the flight, and how quickly you adopt local meal and sleep times on arrival. Light exposure at the right times and strategic use of melatonin can cut recovery time noticeably — that's exactly what this jet lag calculator is designed to help with.

Eastward travel is generally harder on your body than westward travel. When you fly east, you need to advance your internal clock — going to sleep and waking earlier than your body naturally wants to. Most people have a circadian rhythm that runs slightly longer than 24 hours, which means it's easier to delay (stay up later) than to advance (get to sleep earlier). Flying west mimics a natural day extension. Research suggests eastward jet lag recovery takes roughly 20–30% longer than the equivalent westward journey, which is why our recovery formula uses a 1.0× multiplier eastward vs. 0.8× westward. Practically, this means a New York → London traveller (5 time zones east) may feel full symptoms for 5 days, whereas the return trip could clear in 4.

Melatonin for jet lag is most effective when taken at the right time rather than at a high dose. The research-backed sweet spot for melatonin jet lag dosage is 0.5 mg to 3 mg — far lower than the 5–10 mg tablets commonly sold in pharmacies. Higher doses don't improve effectiveness and may cause next-day grogginess. Timing is everything: take melatonin about 60 minutes before your target bedtime at your destination, not at your old home bedtime. For eastward travel, start taking it on the first night you arrive and continue for 3–5 nights as your body adjusts. For westward travel, it's less essential but can help if you're crossing 5 or more time zones. Always consult a doctor or pharmacist before using melatonin, especially if you take other medications or have health conditions.

The most effective jet lag remedies combine several strategies rather than relying on a single fix. Light exposure is arguably the most powerful tool — bright morning light after eastward travel or evening light after westward travel helps reset your internal clock faster than anything else. Hydration matters too: cabin air is extremely dry (~10–20% humidity), and even mild dehydration intensifies jet lag symptoms like headaches and fatigue. Skip the in-flight alcohol and caffeine; both dehydrate you and fragment sleep. Meal timing at your destination is also surprisingly effective — eating breakfast and dinner on local time signals your gut clock to synchronise. Exercise, particularly a short outdoor walk in sunlight on day one, combines light therapy with physical reset. Finally, resist napping longer than 20 minutes during the day, which can anchor your old time zone and drag out recovery.

Most people begin to notice jet lag symptoms — fatigue, difficulty sleeping, difficulty staying awake, brain fog, digestive upset — after crossing 2 or more time zones. Below 2 zones, most healthy adults adapt within a day without noticing significant disruption. Crossing 3–4 time zones produces clear but manageable symptoms, while 5 or more time zones is where jet lag becomes meaningfully disruptive for the majority of travellers. At 7+ time zones (think London to Bangkok, or New York to Tokyo) the misalignment between your internal clock and local day/night is so large that symptoms like full day-night reversal, mood changes, and impaired concentration are common. This calculator uses these thresholds to classify your trip as mild (1–3 zones), moderate (4–6 zones), or severe (7+ zones), giving you an appropriately scaled recovery plan.