- Why is flying east worse than flying west?
- Your circadian rhythm has a natural period slightly longer than 24 hours (about 24.2 hours on average), which means it's easier for the body to delay sleep than to advance it. Flying east forces you to fall asleep and wake earlier than your body expects — an advance, which is the hard direction. Flying west lets you stay up later and sleep in — a delay, which is the easy direction. The 1-day-per-zone (east) vs 2/3-day-per-zone (west) ratio in this calculator reflects that asymmetry, and matches what aviation-medicine guidelines (FAA, NASA Ames Fatigue Countermeasures, BMJ travel-medicine reviews) publish.
- How accurate is the recovery estimate?
- It's an average-case estimate, not a personalized prescription. Real recovery varies with age (older travelers recover slower), sleep debt going in, in-flight sleep, alcohol and caffeine intake, and personal chronotype (early birds adjust eastbound faster; night owls adjust westbound faster). The numbers here are what a healthy adult flying with no pre-existing sleep debt typically experiences. Treat them as a planning baseline — pad an extra day if you have a high-stakes meeting on arrival.
- Does melatonin actually work for jet lag?
- For eastbound travel, yes — there's solid evidence that 0.3–0.5 mg taken 30 minutes before destination bedtime helps advance the circadian rhythm faster. For westbound travel, melatonin is much weaker because you're trying to delay your clock, not advance it; timed bright-light exposure (afternoon and early evening) does more of the work. Use the lowest effective dose. Higher doses (3–10 mg) are not more effective and can leave you groggy the next day.
- Should I start adjusting my schedule before I leave?
- Yes — that's the highest-leverage intervention. Start 2–4 days before departure (the calculator suggests a number based on how many zones you're crossing). Going east, shift bedtime and wake time 1 hour earlier each day. Going west, shift them 1 hour later each day. By the time you board, you've already done half the work — the body clock has a head start instead of starting from zero.
- What about long-haul flights with a stopover?
- Treat the trip as a single shift from origin to final destination. The stopover layover doesn't help your body clock — it stays on origin time until you start eating and sleeping on destination time. The math doesn't change. The one exception: a stopover long enough to actually sleep on destination time (say, 24 hours at the midpoint) can break the adjustment into two smaller shifts, but most stopovers are too short for this.
- I'm flying back home after only a few days — is it worth adjusting?
- For a short trip (under 3–4 days), many travelers find it better NOT to fully shift to destination time. Stay close to your home schedule (eat, sleep, take meetings on origin time when possible), and you'll have less of a return-jet-lag rebound. This works best for moderate-zone shifts (3–6 hours); for trans-Pacific or trans-Atlantic round trips, you'll still feel something either way.
- Why does the calculator only go up to 12 zone difference?
- The Earth is round, so a 14-hour eastbound shift is biologically the same as a 10-hour westbound shift — your body clock will adjust whichever way is shorter. The calculator normalizes to the shortest direction, so the diff caps at 12 hours. If you're flying New York (UTC-5) to Tokyo (UTC+9), the raw difference is 14 hours east, but the calculator shows 10 hours west — which matches your body's biology and the actual flight path (most NYC-Tokyo routes fly west over the Arctic, not east).
- Does the calculator account for daylight saving time?
- No — it uses raw UTC offsets, and you pick the current offset for each zone. During a DST transition you'd pick the summer offset (e.g. UTC-4 for New York in July, UTC-5 in January). If you're traveling across a DST cutover during the trip, treat it as one additional hour of shift in the relevant direction.
- Is this medical advice?
- No. This is a planning tool based on standard aviation-medicine guidance, not a personalized treatment plan. If you have a diagnosed sleep disorder (insomnia, sleep apnea, circadian rhythm disorder), are pregnant, take prescription medications, or are considering melatonin for a child, ask a doctor before using the schedule-shift and melatonin parts of the plan.
