{
  "id": "jet-lag",
  "version": "b0f14b9657d7",
  "status": "published",
  "name": "Jet Lag Calculator",
  "question": "How long is my jet lag recovery?",
  "summary": "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.",
  "category": "days",
  "subcategory": "time-and-hours",
  "url": "https://www.acalculator.org/days/jet-lag-calculator",
  "markdown": "https://www.acalculator.org/days/jet-lag-calculator.md",
  "kind": "function",
  "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."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "h": {
        "title": "Time difference (hours)",
        "description": "How many hours the destination clock is ahead of or behind home, such as 6 for New York to Paris.",
        "type": "number",
        "minimum": 0,
        "maximum": 12
      },
      "dir": {
        "title": "Direction",
        "description": "East when the destination clock is ahead of home, west when it is behind.",
        "type": "string",
        "enum": [
          "east",
          "west"
        ]
      },
      "pre": {
        "title": "Days of shifting sleep before the trip",
        "description": "Days before you leave on which you go to bed 1 hour earlier (east) or later (west), 0 to 3.",
        "type": "integer",
        "minimum": 0,
        "maximum": 3
      },
      "arr": {
        "title": "Arrival date",
        "description": "The day you land. Leave it empty to skip the date.",
        "type": "string",
        "format": "date"
      }
    }
  },
  "outputs": {
    "days": {
      "label": "Days to adjust",
      "description": "Hours still to shift ÷ hours a day, rounded up to whole days.",
      "format": "integer"
    },
    "exactDays": {
      "label": "Days to adjust, unrounded",
      "description": "Hours still to shift ÷ the daily rate.",
      "format": "number"
    },
    "left": {
      "label": "Hours to shift after landing",
      "description": "The time difference less the hours shifted before the trip.",
      "format": "number"
    },
    "rate": {
      "label": "Adjustment rate",
      "description": "Hours a day the body clock shifts.",
      "format": "text"
    },
    "adjusted": {
      "label": "Adjusted by",
      "description": "The arrival date plus the days to adjust.",
      "format": "date"
    },
    "summary": {
      "label": "Answer",
      "description": "The answer in one sentence.",
      "format": "text"
    },
    "note": {
      "label": "Note",
      "description": "Whether this trip is likely to cause jet lag.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "h": 6,
      "dir": "east",
      "pre": 0,
      "arr": "2026-10-02"
    },
    "outputs": {
      "days": 6,
      "exactDays": 6,
      "left": 6,
      "rate": "1 hour a day (east)",
      "adjusted": "2026-10-08",
      "summary": "Your jet lag recovery takes about 6 days after flying east across 6 hours of time difference",
      "note": "Expect jet lag: 2 or more time zones crossed."
    },
    "text": "Your jet lag recovery takes about 6 days after flying east across 6 hours of time difference."
  },
  "examples": [
    {
      "given": {
        "h": 6,
        "dir": "east",
        "pre": 0
      },
      "expect": {
        "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); hand calculation in content.mdx: 6 hours ÷ 1 hour a day = 6 days"
    },
    {
      "given": {
        "h": 6,
        "dir": "west",
        "pre": 0,
        "arr": "2026-10-02"
      },
      "expect": {
        "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); hand calculation in content.mdx: 6 ÷ 1.5 = 4 days; 2 October + 4 days = 6 October"
    },
    {
      "given": {
        "h": 8,
        "dir": "west",
        "pre": 3
      },
      "expect": {
        "days": 4,
        "exactDays": 3.3333333333333335,
        "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); hand calculation in content.mdx: 8 − 3 = 5 hours ÷ 1.5 = 3.33, rounded up to 4 days"
    },
    {
      "given": {
        "h": 1,
        "dir": "east",
        "pre": 0
      },
      "expect": {
        "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); hand calculation in content.mdx: 1 hour ÷ 1 = 1 day; under two time zones"
    }
  ],
  "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)"
  ],
  "related": [
    "sleep",
    "time",
    "time-duration"
  ],
  "changelog": []
}