Starlight Tools

Jet Lag Calculator and Recovery Planner

Enter your route, departure and arrival timing, trip length, usual sleep window, and adjustment preference to estimate recovery days, eastbound or westbound direction, sleep timing, light exposure, caffeine cutoff, nap advice, meal cues, and short-trip strategy. All calculations run locally in your browser.

Calculator

Results

Ready to calculate
Use the controls on the left and calculate to see your result, units, and interpretation.

About This Tool

Crossing time zones is not just a travel logistics problem. It is a body-clock problem. This jet lag calculator turns your route, departure timing, arrival timing, trip length, usual sleep window, and adjustment preference into a practical recovery itinerary.

The planner estimates the effective clock shift by comparing origin and destination timezone offsets on the selected arrival date. That matters because daylight saving rules can change the real adjustment by an hour or more. It then labels the direction as eastbound, westbound, or minimal shift, estimates recovery days, and builds either a pre-trip schedule in origin time or an after-arrival schedule in destination time.

The output includes daily bedtime and wake time, local body-clock mismatch, bright-light seeking, bright-light avoidance, dim evening light, caffeine cutoff, nap advice, meal timing cues, target stable date, and a short-trip recommendation when the stay is too brief for full adaptation. Eastbound travel often needs more deliberate clock advancing; westbound travel often adapts faster because delaying sleep is usually easier.

This tool is also a planning aid rather than a medical tool. It does not diagnose sleep disorders or account for medications, light therapy devices, or unusual work rosters. What it does provide is a clean, timezone-aware framework for sleep timing decisions. Used alongside your existing route and schedule planning, it gives you a more realistic idea of when you will feel aligned with the local clock and when you may still be working against it.

Formula

  • timezone difference = destination offset - origin offset
  • normalized shift = shortest east-west clock shift from -12 to +12 hours
  • estimated recovery days = ceil(abs(normalized shift) / effective daily adjustment pace)
  • after-arrival destination bedtime = usual bedtime + remaining body-clock mismatch
  • pre-trip origin bedtime = usual bedtime - completed adjustment toward destination time

Worked Examples

New York to Paris eastbound

Inputs: America/New_York to Europe/Paris, 23:00-07:00 usual sleep, standard eastbound pace. The effective shift is about +6 hours, so recovery is about 6 days. In destination time, the first nights trend from a body-clock bedtime around 05:00 toward 23:00; seek morning light and keep evenings dim.

Los Angeles to Tokyo route interpretation

Inputs: America/Los_Angeles to Asia/Tokyo. The raw offset can look like a next-day jump, so the calculator normalizes it to the shortest east-west body-clock shift. Depending on daylight saving date, it may behave like a large westbound delay; first two days usually need evening light and early-morning light avoidance.

London to New York westbound

Inputs: Europe/London to America/New_York, 23:00-07:00 sleep. A -5 hour shift often adapts faster than an equivalent eastbound trip. Early destination bedtimes gradually move later; seek late afternoon light, avoid bright early morning light, and stop caffeine well before target bedtime.

Two-night business trip

Inputs: 5-6 hour shift, two nights at destination, important meeting on day two. Full adaptation is unlikely before departure, so the short-trip recommendation favors partial adjustment, strategic light around work hours, short naps only when needed, and a return plan if you did adapt.

Method and Sources

This calculator estimates recovery from the normalized time-zone shift, travel direction, selected pace, chronotype preference, age sensitivity, and circadian timing cues. It treats light as a major clock-reset cue, caffeine as an alertness tool with a conservative cutoff, and naps as short recovery breaks rather than a replacement for the target sleep window. It is informational planning support, not medical advice.

CDC Travelers' HealthJet lag guidance on adjusting sleep before travel, destination routines, caffeine timing, hydration, and short naps.
Sleep FoundationJet lag overview explaining circadian mismatch, recovery variability, light timing, melatonin timing, and short-trip tradeoffs.
Mayo ClinicTreatment guidance separating eastward and westward light strategies and cautioning against late caffeine.

FAQs

How many days does jet lag last?

A practical estimate is the number of time zones crossed divided by your daily adjustment pace. Many travelers feel mostly adjusted after several days, but direction, sleep timing, light exposure, age, and chronotype can change the experience.

Is jet lag worse going east or west?

Eastbound trips are often harder because they ask the body clock to advance earlier. Westbound trips often feel easier because delaying sleep is usually more natural, although long westbound trips can still be disruptive.

When should I get sunlight after flying east?

For many eastbound trips, morning or mid-morning destination light helps advance your clock. For large shifts, very early morning light can be mistimed, so the calculator labels seek-light and avoid-light windows separately.

When should I avoid light?

Avoid bright light when it would push your body clock the wrong way: usually late evening for eastbound recovery and early morning for westbound recovery. Keep the final two hours before target bedtime dim.

Should I take melatonin for jet lag?

Melatonin timing can affect the body clock, but it is not appropriate for everyone and regulations vary by country. Ask a clinician or pharmacist before using it, especially if you take medication or have a sleep disorder.

How late can I drink caffeine?

Use caffeine early enough to protect the next sleep window. This planner gives a conservative cutoff about eight hours before target bedtime and flags daytime use as a tool for alertness rather than clock-resetting.

Should I nap after arrival?

Short naps can help if you are very sleepy, but keep them brief and avoid late-day naps that compete with the first planned local bedtime.

What if my trip is only two or three days?

If the stay is shorter than the estimated recovery window, full adaptation may not be worth it. Partial adjustment or staying closer to home time can be more practical for a short business trip.

Do layovers count?

Usually the destination time zone matters most unless the layover is long enough for a real sleep period or meaningful daylight exposure. Enter the place where you need to function after arrival.

Does crossing the International Date Line matter?

The calendar date may jump, but jet lag depends on the effective clock shift after normalizing the time-zone difference to the shortest east-west adjustment.

Does this tool use external travel data?

No. Everything runs client-side in your browser using built-in timezone rules, with no external APIs or uploaded itinerary data.

Is this medical advice?

No. It is a planning tool based on clock differences and gradual sleep, light, caffeine, nap, and meal timing cues, not individualized medical guidance.

5 Facts

Human circadian rhythms drift slightly longer than 24 hours

That is one reason delaying sleep often feels easier than advancing it after eastbound travel.

Body clock

Cabin light exposure matters

Even without crossing more time zones, poorly timed light can reinforce the wrong local schedule after arrival.

Travel habits

Performance dips often appear on day two

The first day can feel manageable on adrenaline, while the deeper sleep-pressure mismatch shows up after the first local night.

Recovery pattern

Meal timing is a useful cue

Regular meals at destination times help reinforce your new schedule alongside light and sleep timing.

Routine design

Short-haul trips still create social jet lag

Even a modest shift can disrupt meetings and alertness if it lands against your habitual bedtime.

Business travel

Important Note

This planner is informational only. If you have a diagnosed sleep condition, take medication affecting alertness, or need medical clearance for travel, use this output only as a scheduling reference and speak to a qualified clinician for personalized advice.

Explore more tools