# How long is my jet lag recovery?

Estimates jet lag recovery days from the hours of time difference and the direction you fly, at the CDC’s average of 1 hour a day eastward and 1.5 hours a day westward, less any hours you shift before the trip.

- Page: https://www.acalculator.org/days/jet-lag-calculator
- JSON spec: https://www.acalculator.org/days/jet-lag-calculator.json
- Version: b0f14b9657d7

## Default answer

Example with the default inputs (Time difference (hours) 6, Direction East (clock ahead), Days of shifting sleep before the trip 0, Arrival date October 2, 2026) on the example date Friday, October 2, 2026: Your jet lag recovery takes about 6 days after flying east across 6 hours of time difference.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| h | Time difference (hours) | How many hours the destination clock is ahead of or behind home, such as 6 for New York to Paris. |
| dir | Direction | East when the destination clock is ahead of home, west when it is behind. |
| pre | Days of shifting sleep before the trip | Days before you leave on which you go to bed 1 hour earlier (east) or later (west), 0 to 3. |
| arr | Arrival date | The day you land. Leave it empty to skip the date. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| days | Days to adjust | Hours still to shift ÷ hours a day, rounded up to whole days. |
| exactDays | Days to adjust, unrounded | Hours still to shift ÷ the daily rate. |
| left | Hours to shift after landing | The time difference less the hours shifted before the trip. |
| rate | Adjustment rate | Hours a day the body clock shifts. |
| adjusted | Adjusted by | The arrival date plus the days to adjust. |
| summary | Answer | The answer in one sentence. |
| note | Note | Whether this trip is likely to cause jet lag. |

## Method

Days to adjust = (time difference − hours shifted before the trip) ÷ rate, rounded up; rate = 1 hour a day east, 1.5 west.

## Assumptions

- The CDC’s average rates: the body clock shifts 1 hour a day after flying east and 1.5 hours a day after flying west.
- Each day of shifting sleep before the trip moves the body clock 1 hour toward the destination.
- People vary; light, sleep and timing change how fast you adjust.

## Worked examples

1. h = 6, dir = east, pre = 0 gives days = 6, exactDays = 6, rate = 1 hour a day (east), summary = Your jet lag recovery takes about 6 days after flying east across 6 hours of time difference. Source: Riedy and Williams, Jet Lag Disorder, CDC Yellow Book 2026 (average adaptation 1.5 hours a day westward and 1 hour a day eastward; jet lag follows travel across at least two time zones; shifting sleep 1 hour a day for 2 to 3 days before the trip reduces the time to adjust), https://www.cdc.gov/yellow-book/hcp/travel-air-sea/jet-lag-disorder.html (retrieved 2026-10-02).
2. h = 6, dir = west, pre = 0, arr = 2026-10-02 gives days = 4, exactDays = 4, adjusted = 2026-10-06. Source: Riedy and Williams, Jet Lag Disorder, CDC Yellow Book 2026 (average adaptation 1.5 hours a day westward and 1 hour a day eastward; jet lag follows travel across at least two time zones; shifting sleep 1 hour a day for 2 to 3 days before the trip reduces the time to adjust), https://www.cdc.gov/yellow-book/hcp/travel-air-sea/jet-lag-disorder.html (retrieved 2026-10-02).
3. h = 8, dir = west, pre = 3 gives days = 4, exactDays = 3.333333, left = 5. Source: Riedy and Williams, Jet Lag Disorder, CDC Yellow Book 2026 (average adaptation 1.5 hours a day westward and 1 hour a day eastward; jet lag follows travel across at least two time zones; shifting sleep 1 hour a day for 2 to 3 days before the trip reduces the time to adjust), https://www.cdc.gov/yellow-book/hcp/travel-air-sea/jet-lag-disorder.html (retrieved 2026-10-02).
4. h = 1, dir = east, pre = 0 gives days = 1, note = Under 2 hours of difference: jet lag disorder is not expected.. Source: Riedy and Williams, Jet Lag Disorder, CDC Yellow Book 2026 (average adaptation 1.5 hours a day westward and 1 hour a day eastward; jet lag follows travel across at least two time zones; shifting sleep 1 hour a day for 2 to 3 days before the trip reduces the time to adjust), https://www.cdc.gov/yellow-book/hcp/travel-air-sea/jet-lag-disorder.html (retrieved 2026-10-02).

## FAQ

### How long does jet lag recovery take?

On average the body clock shifts about 1 hour a day after flying east and 1.5 hours a day after flying west (CDC Yellow Book). A 6-hour trip east takes about 6 days; the same trip west takes about 4.

### Why is flying east worse than flying west?

Flying east means going to bed earlier by your body's clock, which is harder than staying up later. The body's own daily rhythm runs a little longer than 24 hours, so most people find it easier to delay their clock than to advance it.

### How many time zones cause jet lag?

The CDC describes jet lag disorder after travel across at least two time zones. With a 1-hour difference you may feel a little off for a day, but jet lag disorder is not expected.

### Can I adjust before I leave?

Yes. The CDC says shifting your sleep 1 hour a day toward the destination time in the 2 to 3 days before the trip (earlier for east, later for west) can shorten the time to adjust. Each day you shift takes 1 hour off the difference here.

### What helps me adjust faster after I land?

Light at the right time. Bright morning light helps the clock move earlier, which helps after flying east; evening light helps it move later, which helps after flying west. Keep to local meal and sleep times.

### What if the time difference is more than 12 hours?

This page takes up to 12 hours. A clock 14 hours ahead is also 10 hours behind, so type the shorter difference and the direction that matches it.

## Sources

- Samantha M. Riedy and Scott G. Williams, Jet Lag Disorder, CDC Yellow Book 2026 (travel across at least two time zones; average rate of adaptation 1.5 hours a day westward and 1 hour a day eastward; shifting sleep 1 hour later for westward or earlier for eastward travel per day in the 2 to 3 days before the trip may reduce the time to adjust; morning light promotes phase advances, evening light phase delays). https://www.cdc.gov/yellow-book/hcp/travel-air-sea/jet-lag-disorder.html (retrieved 2026-10-02)