Nobody sleeps well when the clock disagrees with the sky. You land, it is 7am where you are standing, your body is convinced it is 11pm, and you have a seminar at nine.
This planner takes where you are leaving, where you are landing, how long you are in the air, and which way you are travelling, then hands back a schedule for shifting your sleep before you go plus recommendations for the flight and the first few nights. It is arithmetic on time zones wrapped around a set of well-worn rules about light and caffeine. It is not a sleep doctor.
Plan for jet lag when traveling across time zones. Get an adjustment schedule and sleep recommendations based on your flight details.
How it works
Pick your departure zone, your arrival zone, the flight duration in hours, and the direction, then press Plan Jet Lag. The tool reads both zone offsets, takes the difference, and reports it with a sign, so New York to London comes out as +5 hours. It refuses the two inputs that would produce nonsense: the same zone on both sides, and a duration that is not a positive number.
The schedule length comes from one rule. Take the size of the gap, divide by 1.5, round up. A five hour gap gives ceil(5 / 1.5) = ceil(3.33) = 4 days. A sixteen hour gap gives ceil(16 / 1.5) = ceil(10.67) = 11 days. Bigger gap, longer runway, and the 1.5 hours a day rate is the assumption sitting underneath every number the tool prints.
What you do depends on the direction box. Eastward means shift sleep earlier, seek morning light, and cut caffeine after 2pm local. Westward means go to bed later, seek evening light, and stay awake until local bedtime. On the flight, anything over 6 hours is told to sleep about 60% of the journey and anything shorter to stay awake with short naps. The first night you sleep at local bedtime.
A worked example
New York to London, 7 hours in the air, eastward. The gap is +5 hours, so the adjustment runs ceil(5 / 1.5) = 4 days. Four days before you fly you start going to bed an hour earlier each night, you go out for morning light when you land, and you stop caffeine after 2pm. The flight clears 6 hours, so the plan calls for round(7 x 0.6) = round(4.2) = 4 hours of sleep on board, then local bedtime that first night and full adjustment around day four.
Los Angeles to Tokyo, 11 hours, eastward. Tokyo sits at UTC+9 and Los Angeles at UTC-7, a gap of 16 hours, so the plan stretches to 11 days of shifting and round(11 x 0.6) = round(6.6) = 7 hours on the aircraft. Sixteen hours is about as bad as a single hop gets, and 11 days is the honest answer rather than a reassuring one.
Run it backwards, London to New York, 8 hours westward, and the gap reads -5 hours with the same 4 days attached, but every instruction flips: bed an hour later each night, evening light, stay up until local bedtime. Same size of gap, opposite advice, which is why direction is a separate field.
Common mistakes and honest caveats
The direction box is not linked to the zones, and nothing checks that they agree. Choose New York to Tokyo and leave the direction sitting on westward, and you get a westward checklist bolted onto a sixteen-hour eastward jump. The schedule follows the direction field, so set both of them deliberately.
Second, the offsets are read at the moment you press the button, not on your travel date. If your trip falls either side of a clock change in one of the two zones, the real gap will be an hour larger or smaller, and the day count can move by one with it.
The 1.5 hours a day figure is a rule of thumb and nothing more, and eastward is the harder direction for most people because falling asleep earlier is harder than staying up later. The caffeine cut-off and the light advice are general guidance rather than personal instruction. Health Canada and the CDC both publish jet lag advice, and anyone with an ongoing sleep problem should follow that instead of a dropdown. This is a planning guideline, not medical advice.
Other tools
Getting back into a rhythm is the second half of the problem. The morning routine planner rebuilds the start of your day, the night before exam checklist covers the evening before an exam, and the laundry day planner deals with the pile that grew while you were away.
Frequently asked questions
How many days before my flight should I start?
Whatever the plan gives you, counted backwards from departure. Four days means you begin four days before you fly, moving an hour at a time rather than trying to jump the whole gap in a single night.
Which direction is harder?
Eastward, for most people. Going east means falling asleep earlier than your body wants, which is the awkward direction, and the plan responds with morning light instead of evening light.
What does the flight duration actually change?
Two things. It picks your in-flight sleep advice, anything over 6 hours means sleep roughly 60% of the journey and anything under means stay awake with short naps, and it is printed back in the result so you can confirm you typed the right number.
Does it know my exact itinerary?
No. It takes zones, a duration and a direction, and nothing else. Departure and arrival clock times are yours to work with, because they are on your ticket and not in this tool.
Is any of this medical advice?
No. It is a planning guideline built from common rules of thumb. Official guidance from Health Canada, the CDC, or your own doctor comes first if you have a sleep condition, take medication, or fly often enough that jet lag is stacking up.