Pick your departure and arrival time zones to see how many zones you're crossing, your travel direction, an estimated recovery time, and tailored adjustment tips.
Pick your departure and arrival time zones and click Calculate to see your jet lag estimate
This jet lag calculator compares your departure and arrival time zones to estimate how many zones you're crossing, whether you're traveling eastward or westward, and roughly how many days it may take your body clock to adjust. It's built for travelers who want a quick, practical jet lag recovery estimate before a long-haul flight rather than a vague "you'll probably feel jet lagged" warning.
The calculator finds the current UTC offset of both your departure and arrival time zones and takes the difference to determine the number of zones crossed and the direction of travel. Eastward travel (arrival zone ahead of departure zone) is estimated at roughly one recovery day per time zone crossed, since it requires falling asleep earlier than your body naturally wants to. Westward travel is estimated at about one recovery day per 1.5 time zones crossed, since lengthening your day by staying up later is generally easier for the body's circadian rhythm to handle. The full formula and worked examples are broken down further down this page.
Jet lag affects sleep, digestion, mood, and mental sharpness, and can meaningfully impact the first few days of a trip — whether for a vacation, an important meeting, or a competition. Knowing roughly how many days to budget for adjustment, and which direction-specific habits actually help, lets you plan a more realistic itinerary instead of scheduling demanding activities right after landing.
Anyone flying across multiple time zones can use this tool — from a weekend leisure trip to a demanding, multi-city business itinerary. It's especially useful for travelers who need to perform at their best soon after landing, such as before a big meeting, a competition, or a family event, and want a realistic sense of how many buffer days to plan for.
The exact logic this calculator uses to turn two time zones into a recovery estimate
Westward trips divide by 1.5 instead of 1 because lengthening your day (staying up later) is generally easier on the body's circadian rhythm than shortening it (falling asleep earlier), which is the widely cited reason eastward jet lag typically feels worse than westward jet lag for the same number of zones crossed.
Offsets are read at calculation time, so results automatically reflect daylight saving time changes in either zone.
Eastward/westward here means whether your arrival clock reads later or earlier than your departure clock — not which way your plane physically flies.
Crossing 0 or 1 time zone always shows "Minimal jet lag expected" regardless of direction, since the shift is small enough to barely register for most people.
From picking your time zones to reading your adjustment tips
Choose the time zone you're flying from out of the 16 major world time zones listed, such as New York, London, or Tokyo.
Choose the time zone of your destination. The default preset uses New York as departure and London as arrival.
The calculator compares the current UTC offset of both zones to determine the number of zones crossed and the direction of travel.
See exactly how many time zones you're crossing, whether the shift is eastward or westward, and an estimated number of days to adjust.
Follow the eastward, westward, or minimal-impact tips shown below your result to help plan your sleep schedule around the trip.
Using the calculator's own default scenario — New York to London
Suppose you fly from New York (Eastern Time) to London (GMT/BST), the calculator's own default preset.
A second scenario — flying the return leg westward — shows how the 1.5 divisor changes the outcome for the same number of zones
| Route | Offset Difference | Direction | Zones Crossed | Estimated Recovery |
|---|---|---|---|---|
| New York → London | 5 hours | Eastward ➡ | 5 | 5 days |
| London → Los Angeles | 8 hours | Westward ⬅ | 8 | 6 days |
Explanation: Both trips involve a same-day round-the-world-style time shift, but notice that London → Los Angeles crosses more zones (8) than New York → London (5), yet only takes one extra estimated recovery day (6 vs 5) — because westward travel divides by 1.5 instead of 1. This is the calculator's built-in reflection of the "eastward is harder" sleep-science principle: a westward trip has to cross considerably more time zones before it costs as many recovery days as a shorter eastward one.
What each field in your jet lag estimate actually means
| Result Field | What It Means |
|---|---|
| Time Zones Crossed | The rounded absolute difference, in hours, between your arrival and departure zones' current UTC offsets. |
| Direction | Eastward if your arrival clock reads later than departure, Westward if it reads earlier, None if the zones share the same offset. This reflects clock time, not flight compass heading. |
| Estimated Recovery | "Minimal jet lag expected" for 0–1 zones crossed; otherwise a day count using 1 day/zone eastward or 1 day per 1.5 zones westward. |
| Adjustment Tips | One of three fixed tip lists — eastward, westward, or minimal-impact — shown based on your direction and zones crossed. |
About the "direction" label: remember that eastward/westward describes your body clock's shift, not which way your plane flies. A trip like Los Angeles to Tokyo physically crosses the Pacific heading west, but because Tokyo's clock reads far ahead of Los Angeles's, the calculator classifies it as an eastward shift — the harder-to-adjust-to pattern — with a correspondingly larger estimated recovery figure.
About the adjustment tips: the eastward and westward tip lists are general, direction-specific habits (light exposure timing, bedtime shifts, nap length) rather than a personalized, day-by-day light-exposure schedule — treat them as a starting checklist, not a prescription.
This calculator provides educational estimates only and should not be used as a substitute for professional medical advice. Individual jet lag recovery varies. Consult a healthcare professional for guidance specific to your health situation, especially before long international trips.
Who benefits from a quick, direction-aware jet lag estimate
Plan meeting schedules around an estimated recovery window instead of guessing.
Budget adjustment days before a competition where peak alertness and reaction time matter.
Quickly compare the likely jet lag impact of different routes before booking.
Avoid packing activity-heavy itineraries into the first jet-lagged days of a trip.
Get a fast reference point for how a route's direction and zone count compares to others.
Estimate ramp-up time before jumping into a full workday in a new time zone.
Plan arrival dates with enough buffer before orientation or classes begin.
Anticipate how much recovery time to schedule between international tour stops.
Prepare for time-sensitive negotiations or summits shortly after arrival.
Set realistic expectations for kids' and adults' sleep schedules after landing.
Plan shoot or filing schedules around when you'll realistically be sharp again.
Decide whether to arrive a day early based on the estimated recovery window.
What this jet lag calculator does well, and where it can't replace personal judgment
How the eastward (÷1) and westward (÷1.5) formulas compare as zones crossed increase
| Time Zones Crossed | Eastward Recovery | Westward Recovery |
|---|---|---|
| 0–1 (minimal) | Minimal jet lag expected | |
| 2 | 2 days | 2 days |
| 3 | 3 days | 2 days |
| 4 | 4 days | 3 days |
| 5 | 5 days | 4 days |
| 6 | 6 days | 4 days |
| 8 | 8 days | 6 days |
| 10 | 10 days | 7 days |
| 12 | 12 days | 8 days |
| 16 | 16 days | 11 days |
Summary: This jet lag calculator gives you an instant, free estimate of time zones crossed, travel direction, and recovery days, built on the widely cited principle that eastward jet lag is generally harder to shake than westward jet lag — a useful planning baseline, not a medical guarantee. Pair it with related tools like the Flight Time Calculator and Sleep Cycle Calculator for a fuller trip-planning picture.
Common questions about jet lag and time zone adjustment
Official guidance to complement this calculator — not a substitute for licensed medical advice
Plan the rest of your trip