🌙 Jet Lag Adjustment Calculator

Enter the number of time zones you're crossing and the direction of travel for a rough estimate of adjustment time. This is a general rule-of-thumb estimate, not medical advice.

Time Zones Crossed

Direction

One day a zone east, two-thirds of a day west

The estimate is a flat rate per time zone, with direction changing the rate:

eastward: days = zones × 1.0
westward: days = zones × 0.67

Six zones eastward - New York to Rome - comes out at 6.0 days; the same six going west reads 4.0. The lopsided rate reflects how the body clock moves: it will delay about 1.5 hours a day but advance only about 1, so east is the harder ask.

Zones crossed, not hours flown

A long flight is not automatically jet lag. New York to Santiago is over ten hours and crosses one or two zones. You land exhausted, but your clock is fine by the next morning.
Light is the lever, and its timing flips. Going east, get outside in the morning and dim the evening. Going west, chase late-afternoon light and avoid bright light early.
Past about eight zones east, morning light backfires. It can drag your clock the wrong way round for the first day or two, so keep sunglasses on until mid-morning before switching to the eastward pattern.
Under three days, do not adjust at all. Stay on home time and keep meetings inside your normal waking hours.

A rule of thumb, not medical advice. The tool cannot know what time you land, whether you slept on the plane, your age or chronotype, or that a daylight saving change may add an hour - all of which matter more than the sum.

Frequently asked questions

How long does jet lag last after flying to Europe?

From the US east coast that is five or six zones eastward, so five to six days here. Most people feel functional after two or three and quietly tired in the late afternoon for the rest of the week.

Why is flying east worse than flying west?

Your internal day runs slightly longer than 24 hours, so stretching it is easy and shortening it is not. Westward travel asks you to stay up later; eastward asks you to fall asleep before you are tired.

Should I shift my sleep before the trip?

For eastward flights, yes. Move bedtime and wake time 30 to 60 minutes earlier each day for two or three days and part of the shift is done before you board. Westward, just stay up later on the last night.