Jet Lag Planner: Time Difference and Day-by-Day Plan

How to use it

Choose the Home time zone and the Destination time zone. Type part of a city or region in the box above each list to narrow it.
Set the Travel date, the Departure time at home and the Flight duration (hours).
Enter your Usual sleep time (home time) and Usual wake time (home time). The plan shifts them before you leave.
Read the Time difference, Time zones crossed, Arrival time at destination and Estimated adaptation, then follow the Day-by-day plan.

How the time difference is found

Each zone's UTC offset is read for your travel date from the IANA time zone rules, so daylight saving counts. New York is UTC-4 on July 10 and UTC-5 on November 10, 2026, because US daylight saving ended on November 1. The time difference is the destination offset minus the home offset.

A difference of more than 12 hours is the same as going the other way round the clock, so the planner uses the shorter way: a raw +19 hours from Honolulu to Tokyo becomes -5 hours (westward), and the page says so. The zones crossed are the difference in hours; when it is not a whole number, the page shows a fraction, such as 2.5 for India from Istanbul.

This is a planning aid, not medical advice. Ask a clinician before you use melatonin or any other medicine.

How the day-by-day plan is made

The plan has three parts: the days before departure, the travel day and the days after arrival. Before departure, sleep and wake times move 1 hour a day for up to 3 days, earlier for eastward travel and later for westward travel. The move never exceeds the whole difference, so a 2-hour difference moves 1 hour on the first day and 1 hour on the second. The CDC states that "shifting sleep 1 hour later (for westward travel) or earlier (for eastward travel) per day in the 2–3 days prior to the trip may reduce the amount of time required to adjust to the destination time zone."

The adaptation estimate uses the CDC's average rates: 1 hour a day for eastward travel and 1.5 hours a day for westward travel. The CDC notes that "westward travel is easier to adapt to than eastward travel". The CDC does not give a rule of one day per time zone, so the estimate is the difference divided by the rate, rounded up:

Days to adapt = ceiling(|time difference in hours| / rate), where rate = 1 (eastward) or 1.5 (westward)

Travel day: from departure, meals, sleep and light follow the destination time zone, as the CDC advises during the flight.
Arrival and after: one row for the arrival day and one for each estimated day after it, so the plan runs to the estimate plus one day.
Usual times: from the day of departure, the usual sleep and wake times are shown on destination time.

Light exposure

The CDC states that "exposure in the evening generally promotes phase delays", while bright light in the morning promotes phase advances. The light column of the plan uses the CDC's own example wording for the travel day and the arrival days:

Eastward (clocks ahead): "Get bright light in the early morning" and "Avoid light in the evening".
Westward (clocks behind): "Avoid bright light in the early morning".
On arrival, eastward: "Go outside, getting daylight at your destination time will ease your shift".

What the planner does not cover

The planner gives an estimate for one flight with no stops. It does not cover the following:

Medicines of any kind, including melatonin, sleeping pills and stimulants. The dose and timing of melatonin need a clinician's advice.
Shift work, rotating shifts and night work.
Medical conditions, pregnancy and sleep disorders, which a clinician should assess.
Flights with stops or connections, where each leg can change the clock.
Your own pattern of adaptation: the rates are averages, and people vary.

Example: Istanbul to New York on November 10, 2026

Istanbul is UTC+3 all year, and New York is on EST (UTC-5) on November 10, 2026. The difference is -8 hours: westward, 8 time zones. The estimate is 8 / 1.5 = 5.33, rounded up to 6 days.

With a 10:00 departure and a 10-hour flight you land at 12:00 on November 10, 2026, New York time. With usual sleep at 23:00 and wake at 07:00 at home, the first plan rows are:

Day	Date	Sleep	Wake
3 days before	November 7, 2026	00:00	08:00
2 days before	November 8, 2026	01:00	09:00
1 day before	November 9, 2026	02:00	10:00
Day of departure	November 10, 2026	23:00	07:00

Frequently asked questions

Why does jet lag happen?

Jet lag happens when you cross time zones faster than your body clock can follow. For a while your body keeps home time, so sleep and alertness are out of step with the local day until it adjusts.

Is it harder to adjust after flying east or west?

Usually it is harder after flying east. The CDC gives average rates of 1.5 hours a day for westward travel and 1 hour a day for eastward travel, because most people find it easier to delay than advance the body clock.

Why does the planner use the shorter way round for differences over 12 hours?

A difference of more than 12 hours is the same as going the other way round the clock. Honolulu to Tokyo is +19 hours one way and -5 hours the other, so the planner uses -5 (westward) and says so on the page.

Does the planner take daylight saving into account?

Yes. Each zone's offset is read for your travel date, so New York is UTC-4 in July and UTC-5 in November. Check the date if you travel close to a clock change.

Can I use the plan if I take melatonin?

The planner does not give medicine doses or timing. Melatonin can shift the body clock, but its dose and timing need a clinician's advice, so ask one before you take it.

Why does the plan show two kinds of time?

Before departure you are still at home, so those times are home time. From the day of departure they are destination time, the clock you should live by.

Does the plan work for a trip with stops?

Not fully. The planner covers one flight with one departure time and one flight duration. Each connection can change the clock, so treat a plan for a trip with stops as a rough guide.

Sources

Figures and text last checked on Tuesday, November 10, 2026.