Jet Lag Recovery Calculator

Recovery starts as a rate times a distance and is then whittled down by a chain of multipliers. Flying east costs a full day per time zone; flying west costs about two thirds of a day, reflecting the fact that a body clock running slightly longer than twenty-four hours finds it easier to stay up late than to fall asleep early. Age applies next, in two steps rather than smoothly: nothing below forty-one, a fifteen percent penalty from forty-one, and a thirty percent penalty from fifty-one. Each intervention you switch on then scales the running figure — melatonin multiplies it by seven tenths, strategic light by three quarters — so using both together is multiplicative rather than additive and cuts the estimate to about half. Six zones eastward with both aids and no age penalty resolves to roughly three days; drop melatonin and it becomes five; drop both and you are back at the raw six.

A one-day floor means no combination can return zero. Because the headline number is finally shown as a whole day, small differences vanish: a forty-five year old and a fifty-five year old both read four days on the default trip even though their underlying figures differ by half a day. The pre-trip shift schedule caps at five days regardless of how far you fly, and shifts an hour a day for trips of three zones or fewer, an hour and a half beyond that. Note that the melatonin and light guidance text is chosen by travel direction alone and is printed whether or not you said you would use either.