Jet Lag Planner

What it is for

Jet lag is your body clock running on the old time zone while your watch runs on the new one. You cannot skip it, but you can shorten it by shifting your sleep a little before you leave and by timing daylight, darkness and coffee after you land. This planner turns your route, travel date and normal sleep times into a day-by-day schedule and an .ics file with reminders.

It uses the real offset for your dates, so daylight saving changes are included — a detail that is easy to get wrong by hand in March, April, October and November. It is a planning aid based on rules of thumb, not a medical prediction for you, and it says nothing about melatonin or sleeping pills; ask a clinician about those.

Worked example

Berlin to New York on 10 November 2026, normal bedtime 23:00, wake 07:00, 3 days of pre-adjustment, intermediate chronotype.

The planner reports −6 h, westward: New York is six hours behind Berlin on that date. Over three days at home you go to bed one hour later each night (00:00, 01:00, 02:00) and wake at 08:00, 09:00 and 10:00. That covers 3 h of the shift before departure, so on arrival your body clock is still 3 hours off.

From 10 November you sleep on New York time (23:00–07:00). The "body clock still off by" column drops from 3 to 1.5 to 0, so the planner expects about 2 days to fully adapt after arrival. Last caffeine is 17:00 local time — six hours before bed.

For comparison, London to Tokyo on 2 April 2027 gives +8 h eastward (the UK is already on summer time), the same 3-hour pre-shift, but about 5 days to adapt — eastward travel is slower.

How to read the result

• Time difference and Direction: east means your clock must run earlier (harder), west means later (easier).
• Pre-flight shift: how many hours you absorb at home. Days to adapt after arrival: the remaining gap divided by roughly 1 h/day eastward or 1.5 h/day westward.
• Clock column: pre-flight rows are in home time, post-arrival rows in destination time. Don't mix them up.
• Seek light / Avoid light: built around your estimated body-temperature low point. Light after it pulls your clock earlier, light before it pushes it later.

Tips and common mistakes

• Light windows can fall while you sleep — on the Berlin–New York example the "seek light" window is in the small hours. Do not set an alarm for it; use only the part you are awake for.
• "Avoid light" while awake means dim indoor lights or sunglasses outside, especially in the first eastward mornings.
• Daylight beats indoor lighting by a wide margin. A walk outside does more than a bright office.
• Choose the arrival date carefully for overnight flights: the time difference is measured at arrival, and the post-arrival plan starts on that date.
• For trips of about two days or less, consider staying on home time rather than adapting at all.
• If your city isn't in the list, type its IANA zone (for example America/Halifax) into the "Other" field.

FAQ

Why does eastward travel take longer to recover from?

Most people's internal day is slightly longer than 24 hours, so pushing it later is easier than pulling it earlier. The planner reflects this with 1 h/day of catch-up eastward and 1.5 h/day westward.

What if I can't shift my sleep before the trip?

Set the pre-adjust days to 0. The whole difference then moves to the post-arrival phase, and the plan shows more days of adaptation.

Does it handle daylight saving time?

Yes. Offsets come from the time-zone database for your actual departure and arrival dates, which is why London–Tokyo in April shows +8 h rather than +9 h.

What does chronotype change?

It moves the estimated body-temperature low point (earlier for early birds, later for night owls), which shifts the light windows.