Jet Lag Recovery Calculator
How long jet lag will last and how to adjust.
Reviewed by the Calculation Machine team · Updated 24 October 2026 · How we check our maths
Your values
ⓘ Live results
- Estimated recovery
- 11.9 days
- Direction difficulty
- Harder — you must sleep earlier
- Pre-trip shift per day
- 2.7 hours
- Best light exposure
- Morning light on arrival
- Avoid light
- Late evening
| Tactic | Effect |
|---|---|
| Shift bedtime before travel | Cuts recovery by 1–2 days |
| Time light exposure | Strongest single zeitgeber |
| Skip alcohol in flight | Protects sleep quality |
| Eat on destination schedule | Aligns peripheral clocks |
Quick answer
Your body clock adjusts by roughly one time zone per day flying west and more slowly flying east. This calculator uses about two-thirds of a zone per day eastward, so recovery ≈ zones ÷ 1 going west and zones ÷ 0.67 going east. Crossing 5 zones east, from New York to London, takes about 7.5 days to fully adjust; 3 zones west takes about 3 days.
What the Jet Lag Recovery calculator does
This calculator estimates how long it will take your body clock to catch up with local time after a flight, based on the number of time zones crossed and the direction. It also shows how much you would need to shift your sleep each day before leaving to arrive pre-adjusted, and when to seek or avoid daylight once you land.
Jet lag happens because your internal (circadian) clock keeps running on home time for days after you arrive. Symptoms include poor night sleep, daytime sleepiness, low concentration and stomach upsets. Flying east is usually harder because it forces you to fall asleep earlier than your body wants, and most people's natural clock runs slightly longer than 24 hours, so delaying is easier than advancing.
The figures are averages for adjusting completely; most people feel noticeably better within the first two or three days, and how fast you adapt varies with age, sleep before travel and how much daylight you get. Crossing 3 zones or fewer usually causes only mild symptoms. For a trip of two or three days, many travelers stay on home time instead. Use the flight time calculator to plan the journey and the sleep calculator to pick bedtimes around it.
The formula
Recovery days ≈ zones ÷ 1.0 (westward) Recovery days ≈ zones ÷ 0.67 (eastward) Pre-trip shift per day = zones ÷ preparation days
| Symbol | Meaning | Unit |
|---|---|---|
| zones | Number of hours the local time differs between home and destination | hours / time zones |
| 1.0 and 0.67 | Approximate re-entrainment rate of the body clock westward and eastward | zones per day |
| preparation days | Days before departure you are willing to shift your bedtime and wake time | days |
Adjustment rates of about one hour per day westward and slower eastward are the commonly cited figures in circadian research and in travel-medicine guidance such as the CDC Yellow Book; published estimates range from about 1 to 1.5 days per zone, and this calculator sits at the conservative end for eastward trips. The pre-trip figure spreads the whole time difference over your preparation days; in practice, shifting by more than about 1 hour a day is hard, so for big time differences shift part of the way and finish adjusting on arrival.
Worked examples
New York to London overnight
A business traveler flies 5 time zones east and can start going to bed earlier 3 days before the flight.
Inputs
- Time zones crossed5
- DirectionEastward
- Days before departure to prepare3
Result
- Estimated recovery7.5 days
- Direction difficultyHarder — you must sleep earlier
- Pre-trip shift per day1.7 hours
- Best light exposureMorning light on arrival
- Avoid lightLate evening
Full adjustment takes about 7.5 days, longer than many business trips. Shifting bedtime 1 hour earlier on each of the 3 days before departure, then getting outdoor light in the London morning, can cut that noticeably.
East Coast to West Coast
A family flies 3 zones west, New York to Los Angeles, and shifts bedtime 1 hour later on each of the 3 nights before.
Inputs
- Time zones crossed3
- DirectionWestward
- Days before departure to prepare3
Result
- Estimated recovery3 days
- Direction difficultyEasier — you stay up later
- Pre-trip shift per day1 hours
- Best light exposureEvening light on arrival
- Avoid lightEarly morning
About 3 days to adjust without preparation, and the 1-hour-per-day shift can have them close to Pacific time on arrival. Evening daylight in Los Angeles helps everyone stay up until local bedtime.
Paris to Los Angeles
A traveler crosses 9 time zones westward with 3 days to prepare.
Inputs
- Time zones crossed9
- DirectionWestward
- Days before departure to prepare3
Result
- Estimated recovery9 days
- Direction difficultyEasier — you stay up later
- Pre-trip shift per day3 hours
- Best light exposureEvening light on arrival
- Avoid lightEarly morning
Around 9 days to adjust fully. Spreading 9 hours over 3 days means 3-hour shifts a day, which few people can manage, so aim for about 1 hour a day before leaving and use evening light on arrival for the rest.
When to seek and avoid daylight
Light is the strongest signal that resets the body clock. Light in your body's early morning moves the clock earlier, and light in your body's evening moves it later. Because your body is still on home time when you land, the right hours depend on how far you have traveled.
| Trip | Seek light | Avoid bright light |
|---|---|---|
| Eastward, up to about 6 zones | Morning at destination | Late evening |
| Eastward, about 8 or more zones | Late morning and early afternoon | Early morning for the first days |
| Westward, up to about 6 zones | Late afternoon and evening | Early morning |
| Westward, about 8 or more zones | Midday and afternoon | Very early morning and late night |
Reducing jet lag before, during and after the flight
- Before: shift bedtime and wake time by about 1 hour a day in the direction of travel for 2–3 days (earlier for eastward, later for westward), and avoid starting the trip short of sleep.
- During: set your watch to destination time when you board, sleep on the plane only if it is night at your destination, drink water and keep alcohol and late caffeine low.
- After: eat meals and go to bed on local time, get outdoors at the times in the table above, and keep naps short (20–30 minutes) and before mid-afternoon.
- Melatonin: timed doses can help some travelers, particularly flying east, but it is a medicine in some countries (prescription-only in the UK) and not suitable for everyone. Ask a doctor or pharmacist before using it.
Time zones and common routes
Count the difference in local time, not the flight length: a 10-hour north–south flight can cause no jet lag, while a 6-hour transatlantic hop crosses 5 zones. Daylight saving changes can add or remove an hour for part of the year. The time zone difference calculator gives the offset for your exact departure time.
| Route | Zones | Direction |
|---|---|---|
| New York → Los Angeles | 3 | West |
| New York → London | 5 | East |
| Los Angeles → London | 8 | East |
| London → Singapore | 8 | East |
| Paris → Los Angeles | 9 | West |
| London → Tokyo | 9 | East |
How to use the Jet Lag Recovery Calculator
- 1Enter the number of hours difference between home and destination time (the time zones crossed).
- 2Choose Eastward or Westward; for routes over 12 zones, count the shorter way round the clock.
- 3Enter how many days before departure you can start shifting your sleep (at least 1).
- 4Use the recovery estimate to plan important meetings or activities, and follow the light timing on arrival.
Frequently asked questions
How long does jet lag last?
Roughly one day per time zone crossed when flying west and longer when flying east. Most people feel much better after 2–3 days, even if full adjustment takes about a week after a 5–8 hour shift.
Why is jet lag worse flying east?
Flying east means falling asleep earlier than your body wants. The human body clock naturally runs slightly longer than 24 hours, so it delays more easily than it advances.
Should I sleep on the plane?
Sleep if it is night at your destination, and try to stay awake if it is daytime there. On overnight eastbound flights, even a few hours of sleep makes the first day easier.
Is it better to stay on home time for short trips?
For trips of two or three days, staying on home time is often easier, especially across many zones. Schedule key meetings for times that are daytime in both places if you can.
Does jet lag happen on north–south flights?
Not if the time difference is small. You may feel tired from the flight itself, but your body clock does not need to shift unless the local time changes.
References
- CDC Yellow Book: Health Information for International Travel – Jet Lag — US Centers for Disease Control and Prevention
- Jet lag: trends and coping strategies (The Lancet, 2007) — Waterhouse J, Reilly T, Atkinson G, Edwards B
- Jet lag — NHS (UK National Health Service)
About this calculator
- Built and reviewed by the Calculation Machine team · How we build and test calculators
- Last reviewed: October 24, 2026
- Report an error