Jet Lag Calculator

What's the difference between East and West?

Travelling east is harder than west. Moving west extends your day — your body naturally adapts to longer days more easily. Moving east shortens your day, which fights against your circadian rhythm. A cross-Atlantic UK → New York flight (west, 5 zones) is significantly easier than UK → Tokyo (east, 9 zones).

What should I know about Recovery Timeline?

A general rule: 1 day of recovery per time zone crossed when travelling east, 0.5 days when travelling west. Crossing 8 time zones east = approximately 8 days for full resynchronisation. For short trips, staying on home time is sometimes better than adapting.

What's the key thing to understand about Accelerating Recovery?

Light exposure is the most powerful circadian reset tool. Get bright light in the morning at your destination (for eastward travel) and avoid bright light in the evening. Melatonin 0.5–1mg taken at local bedtime for 3–4 nights significantly shortens adaptation. Stay hydrated and avoid alcohol.

What's the key thing to understand about Travel Safety and Preparation?

Before any international trip: check the Foreign Commonwealth and Development Office (FCDO) travel advice for your destination at gov.uk/foreign-travel-advice — advisories change frequently. Register your trip with the FCDO if travelling to a high-risk destination. Take two copies of all documents (passport, insurance, bookings) — one in luggage, one left at home with a trusted contact. Share your itinerary with someone at home. Travel insurance is not optional — a single overseas medical emergency can cost tens of thousands of pounds without cover. Always check your policy explicitly covers your specific activities (winter sports, watersports, high-altitude trekking often need separate cover) and any pre-existing medical conditions, since a mismatch here is the most common reason claims get refused.

What should I know about Light Exposure Timing?

Strategic exposure to (and avoidance of) bright light is one of the most effective tools for resetting your body clock, because light is the primary signal your brain uses to set circadian rhythm. The general principle: seeking bright light (ideally natural daylight) helps shift your body clock forward (useful after eastward travel), while avoiding bright light and seeking darkness in the evening helps shift it backward (useful after westward travel) — but the exact timing of when to seek or avoid light depends on how many time zones you've crossed and the direction of travel, since light exposure at the wrong time of your body's internal clock can actually shift it the wrong way or reinforce the old schedule. Wearing sunglasses to avoid bright morning light after an eastward flight, or deliberately getting outside in bright daylight shortly after waking following a westward flight, are both commonly used tactics. Because the correct timing varies by trip specifics, using a dedicated light-exposure schedule (several jet lag apps and calculators generate one based on your flight direction and number of zones crossed) tends to work better than generic 'get some sunlight' advice.

What's the key thing to understand about Pre-Flight Adjustment?

Jet lag recovery doesn't have to start only after you land — gradually shifting your sleep and meal schedule in the days before departure, in the direction of the destination time zone, can meaningfully reduce the adjustment needed on arrival. For an eastward trip (which is generally harder to adjust to, since it requires advancing your body clock rather than delaying it), going to bed and waking slightly earlier each day for a few days before the flight — even by 30-60 minutes a day — gets your internal clock partway to the destination schedule before you've even left. For westward travel, shifting bedtime and wake time later has a similar effect in the opposite direction. This pre-adaptation is most practical for trips of several time zones or more, where the alternative is a much larger single adjustment on arrival, and is most effective when combined with matching light exposure changes and, where relevant, shifting meal times toward the destination schedule in the final days before departure rather than attempting the full adjustment in one go after landing.

Does Melatonin Actually Help With Jet Lag?

Melatonin is one of the most researched and most commonly recommended supplements for jet lag, and the evidence generally supports modest but real benefit when used correctly, though it's not a complete solution on its own. Melatonin is a hormone the body naturally produces in response to darkness as part of its circadian rhythm signalling, and taking a small supplemental dose at the appropriate time in the destination time zone can help nudge the body's internal clock toward the new schedule faster than light exposure and sleep timing alone would achieve, particularly for eastward travel across several time zones, where the body's natural rhythm needs to shift forward, a change research suggests the body generally finds harder to achieve quickly than the backward shift needed for westward travel. Timing matters considerably for melatonin to be effective: it's generally recommended to take a low dose (many studies and most guidance suggest a relatively small amount, well below doses commonly sold, is sufficient) close to the target bedtime in the new time zone, rather than at a time based on the departure time zone, since taking it at the wrong time can actually worsen rather than improve adjustment. Melatonin works best as part of a broader approach that also includes managed light exposure and adjusted meal and activity timing, rather than as a standalone fix, and its effectiveness varies between individuals. People with certain health conditions, or who are pregnant, should check with a doctor before using melatonin supplements, and it's not currently available over the counter in all countries, including some restrictions in parts of Europe.

Worked Example: Adjusting After a Long-Haul Eastbound Flight

Flying from London to Tokyo (roughly 9 hours ahead) typically takes about 1 day of recovery per time zone crossed for eastward travel — so around 9 days to fully re-synchronise, though most travellers feel functional well before full circadian realignment. Eastward travel is generally harder to adjust to than westward travel of the same number of zones, because it requires advancing the body clock (going to sleep earlier than usual), which fights against the body's natural free-running rhythm, which tends to run slightly longer than 24 hours and therefore 'wants' to delay (stay up later) rather than advance. Getting bright light exposure in the new location's morning, and avoiding light in the new evening, is the single most effective lever for speeding adjustment in either direction.

Pre-Flight Light Adjustment Strategy

Shifting sleep and light exposure by even 30-60 minutes per day in the days before a long-haul flight reduces the adjustment needed on arrival. For eastbound travel, going to bed and waking 30-60 minutes earlier each day for 2-3 days before departure, combined with morning light exposure, pre-adapts the body clock in the direction needed; for westbound travel, the same approach works in reverse (staying up and waking later, with light exposure shifted to the evening). This pre-flight adjustment is most useful for trips of 5+ time zones, where full post-arrival adjustment would otherwise take most of a week.

Reference: Estimated Recovery Days by Time Zones Crossed and Direction

The rule of thumb behind this table — roughly a day of recovery per time zone crossed eastward, and somewhat faster for westward travel — is a widely used approximation in sleep medicine rather than an exact formula, and most travellers find the bulk of the felt improvement happens in the first half of the estimated window, with the remaining days being a more gradual fine-tuning of sleep timing.

What should I know about Children and Jet Lag?

Children generally adjust to new time zones somewhat faster than adults on the same route, with many paediatric sleep guides suggesting recovery in roughly half to two-thirds the time an adult needs for the same number of zones crossed, though younger children can also show more disrupted, irritable behaviour during the adjustment window even if the underlying clock resets quickly. Keeping consistent nap and bedtime routines in the new time zone, rather than letting schedule slip entirely for the first few days, is commonly recommended as the single most useful strategy for children specifically.