Home-time and destination-time phase lines converging across recovery daysLive current inputs
Date & Time
Jet Lag Duration Calculator
Estimate circadian realignment time after eastward or westward travel using clock shift, direction-specific adaptation, sleep debt, age-related adjustment, and a bounded light-timing intervention factor.
Estimated realignment duration—
Direction-only duration—
Effective adaptation rate—
Sleep-debt allowance—
Age adjustment factor—
Half-alignment point—
Residual shift after day 3—
Estimated burden—
Circadian convergence curve
Home-time and destination-time phase lines converging across recovery days
The destination phase remains fixed while the modeled body-clock phase approaches it at the effective daily rate. A shaded band marks the entered residual tolerance.
Daily realignment forecast
Residual body-clock offset and expected alignment status by day
The forecast shows the modeled phase gap, cumulative shift, sleep-debt allowance, and tolerance status without claiming a clinical diagnosis.
| Recovery day | Body-clock shift | Residual offset | Tolerance status | Sleep-debt allowance | Direction | Planning note |
|---|
Recovery estimate setup
Use personal observations rather than a universal one-day rule
- Enter the absolute time-zone difference.
- Select eastward or westward travel.
- Use adaptation rates from prior comparable trips when available.
- Record real sleep debt before departure.
- Treat light support as a planned behavior, not guaranteed acceleration.
Circadian logic
Direction and sleep loss are different burdens
Many travelers find eastward phase advance slower than westward phase delay, so the model keeps separate entered rates instead of imposing one universal value.
Sleep debt can impair performance even after the body clock begins shifting. It is therefore added as a recovery allowance rather than converted into more time zones.
Calculation method
Estimate phase realignment from direction-specific daily change
The clock shift is reduced by the entered residual tolerance. Direction selects the baseline adaptation rate; age and bounded light-timing support adjust that rate. Sleep debt adds a separate recovery allowance rather than changing the time-zone distance.
Detailed calculation process and general formulas
r_0 = east ? r_e : r_wf_age = 1 + max(age - 40, 0) / 200r_eff = r_0 * (1 + L/100) / f_aged_phase = max(Z - tau, 0) / r_effd_total = d_phase + S/8Symbols, meanings, and units
- Z
- absolute destination clock shifthours
- r_e, r_w
- entered eastward and westward adaptation rateshours/day
- L
- bounded planned light-timing supportpercent
- tau
- residual offset accepted as alignedhours
- S
- pre-travel accumulated sleep debthours
Recovery interpretation
Read the estimate as a planning range, not a diagnosis
Four outputs describe different parts of the travel burden.
Direction baseline
—Days implied by time-zone shift and selected directional rate.
Personal-rate adjustment
—Entered rate after age and light-support factors.
Sleep-loss burden
—Separate allowance for accumulated sleep debt.
Planning horizon
—Estimated days until the residual phase falls inside tolerance.
Decision takeaway: Protect demanding work until both phase offset and sleep debt have meaningfully improved.
Travel-health checks
Use conservative inputs for safety-critical planning
- Base rates on previous trips when possible.
- Do not use the result to time medication.
- Allow more margin for overnight travel or illness.
- Avoid safety-critical decisions when sleepy regardless of the estimate.
Personal evidence
Observations that improve later estimates
- Actual sleep and wake times
- Destination alertness diary
- Travel direction and cabin schedule
- Light exposure timing
- Days until normal performance returned
Practical applications
Decisions this calculator is designed to support
Nine-hour eastward trip
A traveler advances nine hours with three hours of sleep debt and conservative eastward adaptation.
What the result clarifies: The convergence curve separates circadian movement from sleep-loss recovery.
Six-hour westward trip
A traveler who historically delays 1.5 hours per day compares the burden with an eastward return.
What the result clarifies: Direction-specific rates explain why equal clock shifts may need different buffers.
Worked example
Current-input substitution and reconciliation
Model limitations
This is a simplified educational planning estimate, not medical advice. Individual response varies with chronotype, sleep disorders, flight timing, light exposure, health, medication, age, and behavior. Seek professional guidance for medical conditions or medication timing.
Jet Lag Duration Calculator FAQ
Why can eastward and westward estimates differ?
Phase advance and phase delay can occur at different personal rates, so the calculator keeps separate inputs.
Does light support guarantee faster recovery?
No. The entered factor is a bounded planning assumption; incorrect timing can be ineffective or counterproductive.
Why add sleep debt separately?
Sleep loss affects alertness even though it does not increase the clock difference between locations.
Can I use this to schedule melatonin?
No. Medication and supplement timing should be discussed with a qualified clinician.