Jet Lag Calculator

Estimate your arrival local time and a rough jet-lag adjustment period based on your departure time, flight duration, and time zones crossed.

Jet lag happens because your body's internal clock — the circadian rhythm that governs sleep, alertness, and a range of other biological processes — doesn't reset the moment you land somewhere new; it adjusts gradually, typically at a rate cited as roughly one day per time zone crossed, though this varies meaningfully by individual and by direction of travel, since flying east (which shortens your day) tends to feel harder to adjust to than flying west (which lengthens it).

Knowing your arrival's local time is a separate, simpler problem than knowing how your body will feel once you're there, but they're related in practice: a flight arriving at 2am local time is a very different experience from one arriving at 2pm, even if the flight duration and time zones crossed are identical. Working out that arrival time in your head, especially crossing the International Date Line or an odd half-hour offset zone, is exactly the kind of arithmetic that's easy to get wrong while tired and stressed about travel logistics.

This tool handles both pieces together: enter your departure time, time zone, and flight duration, and it calculates your arrival local time along with a rough, clearly-labeled adjustment estimate based on the time zones crossed. That adjustment figure is a commonly cited rule of thumb, not medical advice — actual recovery time depends on far more than the math alone can capture.

1. Pick your departure date and local time.
2. Choose your departure and arrival time zones.
3. Enter your flight duration in hours.
4. Press Calculate to see arrival local time and an adjustment estimate.