{
  "id": "cow-gestation",
  "version": "7542a66763c6",
  "status": "published",
  "name": "Cow Gestation Calculator",
  "question": "Cow gestation: when is my cow due?",
  "summary": "Computes a cow’s calving date from the breeding date (283 days), the normal calving window of 279 to 287 days, how many days along she is, and when to watch for heat if she did not settle.",
  "category": "biology",
  "subcategory": "animals",
  "url": "https://www.acalculator.org/biology/cow-gestation-calculator",
  "markdown": "https://www.acalculator.org/biology/cow-gestation-calculator.md",
  "kind": "function",
  "method": "Calving date = breeding date + 283 days; normal window = breeding date + 279 to 287 days; next heat = breeding date + 21 days.",
  "assumptions": [
    "The estimate is the average gestation of about 283 days given by Mississippi State University Extension; the window of 279 to 287 days is from Penn State Extension.",
    "Days count from the breeding date as day 0. Breed, the calf’s sex and the cow’s age change the length a little.",
    "A cow that did not settle comes back into heat about one estrous cycle (21 days, typically 18 to 24) after breeding."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "d": {
        "title": "Breeding date",
        "description": "The day the cow or heifer was bred (mated or inseminated).",
        "type": "string",
        "format": "date"
      },
      "on": {
        "title": "Today’s date",
        "description": "The day to count from, to show how far along the cow is.",
        "type": "string",
        "format": "date"
      }
    }
  },
  "outputs": {
    "due": {
      "label": "Estimated calving date",
      "description": "The breeding date + 283 days.",
      "format": "date"
    },
    "earliest": {
      "label": "Earliest normal calving date",
      "description": "The breeding date + 279 days.",
      "format": "date"
    },
    "latest": {
      "label": "Latest normal calving date",
      "description": "The breeding date + 287 days.",
      "format": "date"
    },
    "days": {
      "label": "Days along",
      "description": "Whole days from the breeding date to today’s date.",
      "format": "integer"
    },
    "left": {
      "label": "Days to the estimated calving date",
      "description": "Whole days from today’s date to the estimated calving date; negative once it has passed.",
      "format": "integer"
    },
    "stage": {
      "label": "Where she is now",
      "description": "The stage on today’s date, in one line.",
      "format": "text"
    },
    "heat": {
      "label": "Next heat if she did not settle",
      "description": "The breeding date + 21 days, one estrous cycle later.",
      "format": "date"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "d": "2026-07-21",
      "on": "2026-10-19"
    },
    "outputs": {
      "due": "2027-04-30",
      "earliest": "2027-04-26",
      "latest": "2027-05-04",
      "days": 90,
      "left": 193,
      "stage": "Day 90 of about 283: 193 days to the estimated calving date.",
      "heat": "2026-08-11"
    },
    "text": "Your cow is due to calve about April 30, 2027, between April 26, 2027 and May 4, 2027."
  },
  "examples": [
    {
      "given": {
        "d": "2026-10-01",
        "on": "2026-12-01"
      },
      "expect": {
        "due": "2027-07-11",
        "earliest": "2027-07-07",
        "latest": "2027-07-15",
        "days": 61,
        "left": 222,
        "heat": "2026-10-22",
        "stage": "Day 61 of about 283: 222 days to the estimated calving date."
      },
      "source": "Mississippi State University Extension, Publication 2616, The Estrous Cycle of Cattle (after approximately 283 days of gestation, parturition occurs; the cycle averages 21 days, with a typical range of 18 to 24 days), https://extension.msstate.edu/publications/the-estrous-cycle-cattle (retrieved 2026-10-18); Penn State Extension, Beef Cattle Reproduction and Genetics (typically, gestation ranges between 279 and 287 days), https://extension.psu.edu/animals-and-livestock/beef-cattle/reproduction-and-genetics (retrieved 2026-10-18); hand calculation in content.mdx: 1 October 2026 + 279, 283 and 287 days"
    },
    {
      "given": {
        "d": "2027-06-01",
        "on": "2028-03-08"
      },
      "expect": {
        "due": "2028-03-10",
        "earliest": "2028-03-06",
        "latest": "2028-03-14",
        "days": 281,
        "left": 2,
        "stage": "Day 281: in the calving window (days 279 to 287)."
      },
      "source": "Mississippi State University Extension, Publication 2616, The Estrous Cycle of Cattle (after approximately 283 days of gestation, parturition occurs; the cycle averages 21 days, with a typical range of 18 to 24 days), https://extension.msstate.edu/publications/the-estrous-cycle-cattle (retrieved 2026-10-18); Penn State Extension, Beef Cattle Reproduction and Genetics (typically, gestation ranges between 279 and 287 days), https://extension.psu.edu/animals-and-livestock/beef-cattle/reproduction-and-genetics (retrieved 2026-10-18); hand calculation in content.mdx (2028 is a leap year)"
    },
    {
      "given": {
        "d": "2026-03-15",
        "on": "2026-12-31"
      },
      "expect": {
        "due": "2026-12-23",
        "latest": "2026-12-27",
        "days": 291,
        "left": -8,
        "stage": "Day 291: past the latest normal calving date (day 287). Call your vet."
      },
      "source": "Mississippi State University Extension, Publication 2616, The Estrous Cycle of Cattle (after approximately 283 days of gestation, parturition occurs; the cycle averages 21 days, with a typical range of 18 to 24 days), https://extension.msstate.edu/publications/the-estrous-cycle-cattle (retrieved 2026-10-18); Penn State Extension, Beef Cattle Reproduction and Genetics (typically, gestation ranges between 279 and 287 days), https://extension.psu.edu/animals-and-livestock/beef-cattle/reproduction-and-genetics (retrieved 2026-10-18); hand calculation in content.mdx"
    }
  ],
  "sources": [
    "Mississippi State University Extension, Publication 2616, The Estrous Cycle of Cattle (J. A. Parish, J. E. Larson, R. C. Vann): after approximately 283 days of gestation, parturition occurs; the estrous cycle averages 21 days, with a typical range of 18 to 24 days. https://extension.msstate.edu/publications/the-estrous-cycle-cattle (retrieved 2026-10-18)",
    "Penn State Extension, Beef Cattle Reproduction and Genetics: cattle gestation length can vary based on breed, body condition, age and sex; typically, gestation ranges between 279 and 287 days. https://extension.psu.edu/animals-and-livestock/beef-cattle/reproduction-and-genetics (retrieved 2026-10-18)"
  ],
  "related": [
    "goat-gestation",
    "sheep-gestation",
    "mare-gestation",
    "dog-pregnancy",
    "date"
  ],
  "changelog": []
}