Jet Lag Calculator
Enter where you fly from and to, your flight and your usual sleep times to get the time difference, an estimate of recovery days and a day-by-day plan for shifting your sleep and using light before and after you land.
Before you fly: shift your sleep
| Day | Go to bed | Wake up | Seek bright light | Avoid bright light |
|---|
After you land: local schedule and light
| Day | Sleep (local time) | Seek bright light | Avoid bright light | Body clock still off by |
|---|
This plan is educational and based on general sleep-science rules of thumb (about 1 day per time zone to adapt, light after your body-temperature low advances the clock, light before it delays the clock). It is not medical advice. Talk to a doctor before using melatonin or sleep medication.
How to use the Jet Lag Calculator
- Choose the time zones you fly from and to, for example America/New_York to Europe/Paris.
- Enter the flight: departure date and local time and the flight duration.
- Add your usual bedtime and wake time, then choose how many days you can prepare and how fast to shift.
- Press Create jet lag plan to see the time difference, direction, recovery estimate and arrival time.
- Follow the tables: shift your sleep before the flight, then use the light windows after landing until the plan says Adapted.
How the jet lag plan is worked out
- Time difference = destination UTC offset at arrival − origin UTC offset at departure, so daylight saving time on the flight date is included.
- Direction: a positive difference means flying east (advance your clock), a negative one means west (delay it). If the difference is more than 12 hours, the shorter way round is used: +16 h becomes a delay of 8 h.
- Before the flight, bedtime and wake time move by your chosen step each day (earlier for east, later for west) until the flight or until the full shift is reached.
- After landing, the body clock is assumed to catch up about 1 hour per day going east and 1.5 hours per day going west.
- Light windows are placed around your body-temperature low, about 2 hours before your usual wake time on body time: light in the 3 hours after it advances the clock, light in the 3 hours before it delays the clock.
- Recovery estimate uses the classic rule of about 1 day per time zone, minus the hours you shifted before the flight.
Example: New York to Paris
A flight leaves New York at 18:00 on 19 October 2026 (EDT, UTC−4) and lasts 7 h 30 min. Paris is on CEST (UTC+2), so it is 6 hours ahead and you fly east.
- You land at 05:30 UTC, which is 07:30 in Paris but only 01:30 in New York.
- Shifting 1 hour a day for 3 days moves a 23:00–07:00 sleep to 20:00–04:00 before you fly, so it feels like 04:30 when you land.
- The remaining 3 hours take about 3 days. On day 1 avoid bright light early in the morning and get daylight from about 08:00 to 11:00.
Typical time differences and recovery
| Route (northern summer) | Difference | Direction | Rough recovery without preparation |
|---|---|---|---|
| London → New York | −5 h | West | 3–5 days |
| New York → London | +5 h | East | about 5 days |
| Los Angeles → Tokyo | +16 h (adapt as −8 h) | West-style | 5–8 days |
| London → Dubai | +3 h | East | about 3 days |
| Sydney → London | −9 h | West | 6–9 days |
| Paris → Singapore | +6 h | East | about 6 days |
Frequently asked questions
How long does jet lag last?
A common rule of thumb is about one day per time zone crossed. Flying east across 6 time zones can take around 6 days to adjust fully; westward trips are often a little faster. Shifting your sleep before the flight shortens this.
Is jet lag worse flying east or west?
For most people flying east is harder, because you must fall asleep and wake earlier than your body clock wants. The natural body clock runs slightly longer than 24 hours, so delaying (flying west) is easier than advancing.
How does light help with jet lag?
Light is the strongest signal for the body clock. Bright light in the hours after your body temperature low (normally about 2 hours before you usually wake) moves the clock earlier; light in the hours before it moves the clock later. The plan shows these windows in local time.
What if the time difference is more than 12 hours?
Then it is easier for the body to shift the other way. For example Los Angeles to Tokyo is 16 hours ahead in summer, but adapting by delaying 8 hours, as if flying west, is quicker.
Should I adjust before a short trip?
For trips of 2–3 days across a few time zones many travellers stay on home time instead. For longer stays, shifting 1 hour a day for 2–3 days before flying makes the first days much easier.
Is this medical advice?
No. The calculator uses general rules of thumb from sleep research for education only. Talk to a doctor before using melatonin or sleep medicines, especially if you have a health condition.