Shift your sleep before you fly

Set your home city and your destination, then the date you fly. The planner reads the current offset of both zones and works out the size and direction of the shift. Eastward travel means advancing your clock, going to bed and getting up earlier than usual. Westward means delaying it, staying up and sleeping in.

Choose how many days you can realistically pre-adjust. Each pre-trip day moves your bedtime and wake time by about an hour when you are advancing, and about an hour and a half when you are delaying. Three days of pre-shifting will not cover an eight-hour flight, but arriving three hours less out of phase is worth the effort on the days that matter most.

Work down the table one row at a time. The bedtime and wake time are the targets for that night, the light column is when to seek bright light and when to avoid it, and the caffeine cutoff is eight hours before that night's bedtime. Print the plan if you would rather have it on paper than open on a phone at 3am.

Two things the numbers do not know

The shift is calculated from today's offsets. If either zone crosses a daylight saving boundary between now and your flight, the real gap will be an hour different, so check it again in the converter close to departure. The plan also assumes you land on the departure date. On an overnight flight that arrives the next morning, slide every destination row forward by a day.

The two rules driving this tool are standard circadian guidance rather than anything invented here. Shifting sleep by roughly an hour a day before departure, and using bright light in the morning to advance the clock or in the evening to delay it, both come from the phase response curve to light: the same light exposure moves your body clock in opposite directions depending on when it lands relative to your internal night.

Individual response varies a great deal. Free-running circadian periods differ between people, chronotype changes how much a given light dose does, and a plan that resets one person in three days leaves another dragging for a week. Treat the day counts as an order of magnitude, not a schedule you have failed if you miss it.

Eastward travel really is harder. Most people have an internal day slightly longer than 24 hours, which makes delaying easy and advancing a fight, and that is why this planner uses a slower rate for eastward shifts. For shifts beyond about nine hours eastward, some travellers adapt faster by going the other way and delaying instead, which flips the light advice entirely.

Melatonin is deliberately absent from this plan. Timing and dose are what make it work or backfire, both depend on the individual, and it is regulated differently from one country to the next. That is a conversation for a clinician who knows your history, not a number a web page should hand you.