Jet Lag Calculator
Enter your flights and your usual sleep schedule, and get a plan for the nights before you fly and the days after you land: when to sleep, when to seek bright light, and what a long layover is worth. Everything runs in your browser.
How to use
- Pick the origin and destination time zones. The list comes from your browser's own timezone database, so nothing is looked up on a server.
- Enter the departure date and time in the origin's local clock, and the arrival date and time in the destination's clock. For a red-eye that lands the next morning, pick the arrival date one day later.
- If you have a connection, switch to One stop, pick the stop's zone, enter when you land there, and enter the layover length.
- Set your usual bedtime and wake time at home, then read the plan: nights to shift before you fly, a day-by-day schedule after landing, when to seek bright light, and whether your layover is long enough to bank sleep.
How the schedule works
The shift is the destination's UTC offset minus the origin's, both read at the actual departure and arrival instants from your browser's timezone database, so daylight saving on either end is priced in. A shift past 12 hours wraps to the shorter way around the clock, which is what a trip across the International Date Line really asks of your body.
The plan then follows the rates in the CDC Yellow Book (2026 edition, Jet Lag Disorder chapter): shift your sleep one hour per day for up to three nights before departure, then let your body finish the job at about one hour per day eastward or 1.5 hours per day westward. Each row of the schedule is your usual bedtime and wake time moved by the covered part of that shift.
Light windows come from the same chapter: bright light shortly after waking pushes the body clock earlier, which is what eastward travel needs, while bright light in the evening pushes it later for westward travel. A layover counts as a sleep block when at least two hours of it fall inside the destination's 22:00 to 06:00 night.
This tool is general education, not medical advice. The rates are averages across travelers, and individual clocks differ. For sleep problems that persist past a trip, or before using melatonin or any sleep medication, talk to a clinician.
Frequently asked questions
Do the times I enter get sent anywhere?
No. The timezone list, the offset lookups, and the schedule math all run inside your browser tab, using the timezone data your browser already ships with. Nothing is uploaded, nothing is stored, and the page sets no cookies. Once it has loaded, it keeps working offline. Ad slots on the page are served by third-party networks, which follow their own privacy policies.
Where do the timezone offsets come from?
From your browser's Internationalization API, which carries the IANA timezone database. The calculator reads the UTC offset of each zone at the exact instant you enter, not a fixed offset per zone, so a trip that crosses a daylight saving switch is priced correctly on both ends. The same lookup handles half-hour zones like India and quarter-hour zones like Nepal.
How does a layover change the plan?
A connection changes two things. First, the totals: a two-leg trip with a six-hour ground stop is a longer deprivation than a nonstop flight, and the plan states the real door-to-door time. Second, opportunity: when at least two hours of a layover fall inside the destination's 22:00 to 06:00 night, the plan flags it as a sleep block worth taking seriously, because sleep timed to the destination's night starts pulling your body clock over before you even land.
Why does going west feel easier than going east?
The body's own clock runs slightly longer than 24 hours, so staying up later comes more naturally than falling asleep earlier. The CDC Yellow Book puts average adaptation at about 1.5 hours per day westward against 1 hour per day eastward, and this calculator uses those rates. It is also why an exactly 12-hour shift is planned as westward: the same wall-clock distance adapts faster in that direction.
Is this medical advice?
No. The calculator applies general guidance from the CDC Yellow Book's Jet Lag Disorder chapter to the times you enter. The adaptation rates are population averages, not a personal prescription; age, chronotype, and the trip itself all move the result. For sleep problems that persist past a trip, or before taking melatonin or any sleep aid, talk to a clinician.