Jet Lag Calculator

Pick your origin and destination time zones. The calculator returns the zone difference, a severity band, an estimated recovery window, and direction-aware countermeasures. Eastbound trips are biologically harder than westbound — that's baked into the recovery estimate.

From (departure time zone)

Use the offset your phone shows today. During daylight saving, that's the summer offset (e.g. New York is UTC-4 from March to November, UTC-5 otherwise).

To (destination time zone)

Pick the destination's current offset, not its standard time.

Time-zone difference

5 hours

UTC-5 → UTC+0 · Eastbound (clock advances)

Severity

Moderate

< 3 zones = mild · 3–6 = moderate · > 6 = severe

Estimated recovery

5 days

Eastbound ≈ 1 day per zone · westbound ≈ 2/3 day per zone

Adjustment plan

Pre-flight: starting 3 days before departure, move bedtime and wake time 1 hour per day EARLIER. You're trying to advance your body clock toward the destination.
Light exposure at destination: get bright morning light (outdoors, first hour after waking) and AVOID bright evening light. Morning light pulls the body clock earlier.
Melatonin: 0.3–0.5 mg taken 30 minutes before destination bedtime, for the first 3–5 nights. Eastward is where melatonin actually helps — westward, less so.
Meals: eat on destination time from the moment you board. Skip in-flight meals that don't match the destination schedule. A 12–16 hour fast before destination breakfast helps reset peripheral clocks.
Hydrate: aircraft cabins run at 10–20% humidity. Drink water steadily; skip alcohol and minimize caffeine in flight (both disrupt sleep architecture and worsen post-flight fatigue).

Estimate, not a prescription. Real recovery varies with age, sleep debt, in-flight sleep, alcohol, caffeine, and chronotype. The numbers here are the average case from aviation-medicine guidelines. If you have a sleep disorder, ask a doctor before using melatonin or shifting your schedule aggressively.