How jet lag calculator Works
The one-day-per-zone rule
Travel medicine's working heuristic: recovery takes roughly a day per time zone eastward, about 60% of that westward. Eight zones east is a week of genuinely altered function — worth planning meetings and expectations around rather than pretending day two is normal.
Why east is harder
Your circadian clock runs slightly longer than 24 hours naturally — which makes DELAYING (staying up later, flying west) biologically downhill and ADVANCING (sleeping earlier, flying east) uphill. Eastward travel asks the clock to do the hard direction, zone after zone. This one asymmetry explains nearly every jet lag story difference.
Planning around the curve
Recovery is not linear: days 1–2 are worst, improvement runs roughly half a zone per day. Schedule demanding work for day 3+, build the first two days around light and walks, and reserve big decisions for when your clock and the local one agree. Short-trip travelers face the real choice: shift fully (worth it past 3 days) or ride home-time (smart under 2).