How long does jet lag last?
Last reviewed: July 2026
As a rule of thumb, your body needs about one day per time zone crossed to fully adjust. With a six-hour time difference, that's roughly six days — though the actual duration depends heavily on flight direction, your age and your behavior.
The rule of thumb: one day per time zone
Your internal clock shifts only slowly — about one hour per day. That's why full adjustment takes roughly as many days as the number of time zones you crossed. The first one to two days are usually the worst, after which it noticeably improves.
Eastbound flights take longer than westbound flights
Traveling east means having to sleep earlier — which is hard for your internal clock, since it naturally runs a bit longer than 24 hours. Rule of thumb: about one hour of adjustment per day going east, but up to an hour and a half going west. That's why eastbound flights take longer.
What speeds up recovery
Light at the right time, a sleep schedule switched to destination time right away and, optionally, melatonin can shorten the adjustment. If you ignore the rhythm and take long naps during the day, though, you'll drag out your jet lag.
FAQ
How long does jet lag last after trips to the USA?
With six to nine hours of time difference, adjustment usually takes three to six days. Since it's a westward flight, it tends to go faster than an eastward trip over the same distance.
Why is the first day the worst?
On arrival day, the gap between your internal clock and local time is at its biggest, and you often have sleep to catch up on. Each day the clock shifts a bit more, so it gets better after that.
Does jetlag last the same amount of time for everyone?
No. Age, chronotype, sleep quality, and how consistently you stick to light exposure and local times make a big difference. Older people and early risers often struggle more with eastward flights.
The science behind it
Flyly's plan is based on the phase-response curve of circadian chronobiology — the same model used in sleep research and space medicine for shift work and time zone changes:
- Khalsa, Jewett, Cajochen & Czeisler (2003): A phase response curve to single bright light pulses in human subjects, The Journal of Physiology. doi:10.1113/jphysiol.2003.040477
- Eastman & Burgess (2009): How to travel the world without jet lag, Sleep Medicine Clinics. doi:10.1016/j.jsmc.2009.02.006
- Wittmann, Dinich, Merrow & Roenneberg (2006): Social jetlag: misalignment of biological and social time, Chronobiology International. doi:10.1080/07420520500545979
- Brainard, Barger, Soler, Hanifin et al. (2016): The development of lighting countermeasures for sleep disruption and circadian misalignment during spaceflight, Current Opinion in Pulmonary Medicine. doi:10.1097/mcp.0000000000000329
