Jet Lag Calculator Build my plan

2026 computational chronobiology · FJK oscillator model

Beat jet lag before you land.

Get a personalized, minute-by-minute recovery protocol — precisely timed light, darkness, melatonin, caffeine and meals — engineered from your own body clock to reset you in days, not weeks.

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Free · No sign-up · Runs entirely in your browser

Your trip & sleep profile

Use your habitual, free-day sleep times — not your alarm-clock schedule.

How the jet lag calculator works

This tool models your circadian pacemaker with a simplified version of the Forger–Jewett–Kronauer (FJK) limit-cycle oscillator. It estimates two anchor points from your habitual sleep: your Core Body Temperature minimum (CBTmin), about 2.5 hours before you wake, and your Dim Light Melatonin Onset (DLMO), about 2 hours before bed. Light exposure timed after CBTmin advances your clock, while light before CBTmin delays it.

Based on the direction and size of your time-zone change, the calculator prescribes a single continuous block of bright light and a single block of darkness each day (“bang-bang” control), low-dose melatonin (0.5–1.0 mg), a destination-timed double-caloric breakfast, and direction-specific caffeine timing. Rates are reduced by 25% for travellers aged 50–65 and by 50% for those over 65, and eastward trips of eight or more zones use an antidromic (backward) delay because it re-entrains faster than a large advance.

Frequently asked questions

How does a jet lag calculator work?

It estimates your circadian phase from your habitual sleep times — your Core Body Temperature minimum (CBTmin, about 2.5 hours before wake) and Dim Light Melatonin Onset (DLMO, about 2 hours before bed). It then compares your origin and destination time zones to decide whether you need to shift your clock earlier (a phase advance) or later (a phase delay), and schedules bright light, darkness, low-dose melatonin, meals and caffeine to move your clock as fast as biology allows.

Should I use light in the morning or evening for jet lag?

It depends on direction. Travelling east you need a phase advance, so seek bright light in the destination morning (after your CBTmin) and avoid light in the evening. Travelling west you need a phase delay, so seek bright light in the destination evening (before your CBTmin) and avoid early-morning light.

How much melatonin should I take for jet lag?

A low physiological dose of 0.5–1.0 mg is recommended. Doses of 3 mg or more can spill into the wrong part of the phase-response curve and worsen misalignment. For eastward (advance) trips, take it 2–4 hours before your shifting DLMO.

Why does flying from North America to Asia count as westward?

Circadian adjustment follows the shorter path around the 24-hour clock. If a destination is 16 hours ahead, that is the same as being 8 hours behind — so an 8-hour westward phase delay is the correct, and easier, adjustment, which also matches the physical trans-Pacific westward flight.

How long does it take to get over jet lag?

Untreated, the body clock shifts roughly 1 hour per day after eastward travel and about 1.5 hours per day after westward travel, so a 6-zone trip can take up to a week. A well-timed light, melatonin and meal protocol can roughly halve that, and older travellers shift more slowly so should start pre-flight adjustment earlier.