How does a jet lag calculator work?

It compares the UTC offset of your departure and arrival cities on your travel date, counts the number of time zones crossed, and applies the direction of travel. Eastward flights compress your day and are harder to adjust to, so the recovery estimate is longer than for the same number of zones flown westward.

How many days does it take to recover from jet lag?

A common rule of thumb is roughly one day per time zone crossed when flying west, and up to 1.5 days per zone when flying east. Crossing 8 zones eastward can therefore take 8–12 days to fully resolve, although most people feel functional well before that.

Should I shift my sleep schedule before departure?

For trips crossing four or more time zones, shifting your bedtime by 30–60 minutes per day for three days before departure meaningfully reduces arrival-day symptoms. Shift earlier for eastward travel and later for westward travel.

When should I use light and when should I avoid it?

Light is the strongest signal for your circadian clock. After eastward travel, seek bright morning light and avoid it in the evening. After westward travel, do the opposite: avoid early morning light and get plenty of late-afternoon and evening light.

Is melatonin useful for jet lag?

Reviews of controlled trials find low-dose melatonin (0.5–5 mg) taken close to target bedtime at the destination can shorten adaptation, particularly for eastward travel across five or more zones. Dose and timing matter more than quantity; check with a clinician if you take other medication.

Is the calculator free and does it store my data?

Yes and no, respectively. It is free with no account required, and every calculation runs in your browser — no trip details are sent to a server.

Jet Lag Calculator

Estimate how long jet lag will last on your next flight and get a day-by-day adjustment schedule. Free, no sign-up, and every calculation runs in your browser.

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What the calculator estimates

Time zones crossed

The real UTC offset gap on your travel date, including daylight saving.

Recovery time

Estimated days to full adjustment, weighted by travel direction.

Light & sleep plan

When to seek light, avoid it, and shift bedtime each day.

How jet lag is calculated

Jet lag is the mismatch between your internal circadian clock and local time at your destination. The size of that mismatch is the number of time zones you cross; the difficulty of closing it depends on direction. Your body clock runs slightly longer than 24 hours, so lengthening a day (flying west) is easier than shortening one (flying east).

The calculator resolves the actual UTC offset of both airports on your date of travel using the IANA time zone database, so daylight saving transitions are handled correctly. It then applies roughly one day of recovery per zone westward and up to 1.5 days per zone eastward, and places light exposure windows relative to your estimated circadian low point — the couple of hours before your habitual wake time, when light has the strongest phase-shifting effect.

These are population-level estimates, not medical advice. Individual adaptation varies with age, sleep quality, flight timing, and how strictly you follow the light schedule.

Jet Lag Calculator

What the calculator estimates

Time zones crossed

Recovery time

Light & sleep plan

How jet lag is calculated

Related tools and reading

Jet Lag Planner

Flight Time Calculator

Time Zone Converter

How Long Does Jet Lag Last?

Circadian Rhythm & Travel

Methodology

Frequently Asked Questions

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