See the time difference between your departure point and your destination, roughly how many days it takes to adjust, and practical tips for the direction you're travelling.
Pick the UTC offset where you're leaving from and where you're heading to, and this tool estimates the time difference and roughly how long your body clock will take to catch up.
Jet lag comes from crossing time zones faster than your circadian rhythm - your internal body clock - can keep up. As a rough rule of thumb, most people need roughly one day to adjust for every hour of time difference, though this varies a lot by individual, age and how well you sleep in transit. Direction matters too: travelling east (which effectively shortens your day) tends to be harder to adjust to than travelling west (which lengthens it), because it is generally easier for the body clock to delay itself than to advance it.
Light exposure is the single biggest lever you have. Bright light - ideally daylight - shifts your circadian rhythm, and the direction of the shift depends on timing: morning light after an eastward flight nudges your clock forward, while evening light after a westward flight holds it back. Sleep timing, meal timing and staying hydrated all help too, but light is what does most of the work.
None of this is exact science for any one traveller - some people barely notice a five-hour shift, others feel a three-hour one for days - so treat the estimate here as a starting point for planning the first day or two of a trip, not a guarantee.
Note on daylight saving. This calculator uses standard UTC offsets. If either location observes daylight saving time, the real difference can be an hour more or less depending on the time of year.
This tool gives indicative estimates for planning purposes. Actual prices, rates and times vary – always double-check with an official source before you travel.