Jet Lag Calculator
Find the time difference between two cities on your travel dates and a night-by-night plan for adjusting your body clock.
Result
Fill in the fields above, then press Calculate.
The jet lag calculator works out the time difference between two cities on your travel dates and lays out a simple night-by-night plan for moving your body clock. It uses real time-zone rules, so daylight saving time is applied for the dates you pick, and half-hour zones such as India and Nepal are handled correctly.
Examples
New York to London, 10 to 11 November 2026
New York is UTC-05:00 and London is UTC+00:00, so London is 5 h ahead. Flying east, the body clock has to move 5 h earlier at about 1 hour a day, which is 5 days. With an 11:00 PM bedtime at home, the body-clock bedtime on London time is 3:00 AM, 2:00 AM, 1:00 AM, 12:00 AM, 11:00 PM over nights 1 to 5.
London to New York, 10 to 11 November 2026
Going the other way New York is 5 h behind. Flying west, the body clock moves 5 h later at about 1.5 hours a day, which rounds up to 4 days.
Daylight saving changes the answer: New York to London in March and October
On 15 March 2026 New York has already moved to UTC-04:00 while London is still on UTC+00:00, so the difference is 4 h instead of the usual 5 hours. The same happens on 28 October 2026, after London has changed back but before New York has: 4 h. Those weeks are why this calculator reads real time-zone rules for your dates.
A half-hour zone: New York to Mumbai
India is UTC+05:30, so on 10 to 11 November 2026 the difference is 10 h 30 min. The quicker direction is westward, with 13 h 30 min to shift over 9 days.
Across the date line: Los Angeles to Auckland
On 1 to 3 December 2026 Auckland is 21 h ahead of Los Angeles on the clock, which is the same as 3 h behind on a 24-hour dial. The body clock only has to move 3 h later, about 2 days, even though the local date in Auckland is a day ahead.
Night-by-night plan: New York to London, usual bedtime 11:00 PM
| Night | Body-clock bedtime (London time) | Still to shift |
|---|---|---|
| Night 1 | 3:00 AM | 4 h |
| Night 2 | 2:00 AM | 3 h |
| Night 3 | 1:00 AM | 2 h |
| Night 4 | 12:00 AM | 1 h |
| Night 5 | 11:00 PM | Adjusted |
Time difference from New York in November and in June (2026)
| Destination | November 2026 | June 2026 |
|---|---|---|
| Los Angeles | -3 h | -3 h |
| London | +5 h | +5 h |
| Paris | +6 h | +6 h |
| Dubai | +9 h | +8 h |
| Mumbai / Delhi (Kolkata) | +10 h 30 min | +9 h 30 min |
| Tokyo | +14 h | +13 h |
| Sydney | +16 h | +14 h |
Frequently Asked Questions
How many days does jet lag last?
A common rule of thumb comes from the CDC Yellow Book, which gives an average rate of adaptation of about 1 hour per day eastward and 1.5 hours per day westward. So a 5-hour eastward trip takes about 5 days and a 5-hour westward trip about 4 days. Individuals differ, so treat it as an estimate.
Why is flying east harder than flying west?
The CDC Yellow Book says westward travel is generally easier to adapt to than eastward travel and gives the faster westward rate of about 1.5 hours a day. Flying east asks the body clock to move earlier, which is the slower direction.
When should I get light after a flight?
The CDC Yellow Book says bright light in the morning following the body-temperature low (roughly 2 to 4 hours before your usual wake time) promotes a shift earlier, while evening light generally promotes a shift later. In practice that means morning light after flying east and evening light after flying west.
Does the calculator handle daylight saving time?
Yes. Offsets come from the IANA time-zone database for the departure and arrival dates you enter, so the difference between two cities can change for a few weeks a year when one has moved its clocks and the other has not. The New York to London examples above show it.
What if I am only travelling for a day or two?
The CDC Yellow Book advises that for short trips of less than 2 days you avoid adapting and keep your sleep, activity and eating schedule on your home time zone.
How is a time zone with a 30 or 45 minute offset handled?
Exactly. India is UTC+05:30 and Nepal UTC+05:45, so the difference can include 30 or 45 minutes, and the shift is rounded up to whole days only at the end.
What does the date line change?
The calendar date. When you cross the International Date Line the local date at the destination can be a day ahead or behind, but the body clock only needs to move by the clock-time difference. The result shows the date at the destination when it is noon at the origin.
Which direction should I pick for a very large difference?
Automatic picks whichever direction needs fewer days. If the difference is close to 12 hours the two can be similar, so you can choose a direction yourself. The result notes how many hours the other direction would take.
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Key Terms
- Circadian rhythm
- The body clock that runs on roughly a 24-hour cycle and sets when you feel sleepy and alert.
- Phase advance
- Moving the body clock earlier, as needed after flying east.
- Phase delay
- Moving the body clock later, as needed after flying west.
- IANA time zone
- A named zone such as Europe/London in the shared time-zone database, which records daylight saving rules by date.
Sources
- CDC Yellow Book: Jet Lag Disorder — Centers for Disease Control and Prevention
- IANA Time Zone Database — IANA
Result
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Quick Tips
- •Eastward: morning light tends to help move the body clock earlier, so get outdoors soon after waking and keep the evening lights low.
- •Westward: evening light tends to help move the body clock later, so get bright light in the late afternoon and evening.
- •Eat and plan activities by destination time as soon as you arrive; the CDC Yellow Book lists timing meals, sleep and light by the destination zone among its jet lag tips.
- •For a trip of less than 2 days, the CDC advises keeping your home schedule.