{
  "id": "sheep-gestation",
  "version": "8a9803e2ca3c",
  "status": "published",
  "name": "Sheep Gestation Calculator",
  "question": "Sheep gestation: when is my ewe due?",
  "summary": "Computes a ewe’s lambing date from the breeding date (148 days), the normal lambing window of 144 to 152 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/sheep-gestation-calculator",
  "markdown": "https://www.acalculator.org/biology/sheep-gestation-calculator.md",
  "kind": "function",
  "method": "Lambing date = breeding date + 148 days; normal window = breeding date + 144 to 152 days; next heat = breeding date + 17 days.",
  "assumptions": [
    "The estimate of 148 days is the gestation Alabama Extension plans with; the window of 144 to 152 days is from University of Missouri Extension.",
    "Days count from the breeding date as day 0. Breed and the number of lambs change the length a little.",
    "A ewe that did not settle comes back into heat about one estrous cycle after breeding; Merck gives 16 to 17 days, and the date uses 17."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "d": {
        "title": "Breeding date",
        "description": "The day the ewe 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 ewe is.",
        "type": "string",
        "format": "date"
      }
    }
  },
  "outputs": {
    "due": {
      "label": "Estimated lambing date",
      "description": "The breeding date + 148 days.",
      "format": "date"
    },
    "earliest": {
      "label": "Earliest normal lambing date",
      "description": "The breeding date + 144 days.",
      "format": "date"
    },
    "latest": {
      "label": "Latest normal lambing date",
      "description": "The breeding date + 152 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 lambing date",
      "description": "Whole days from today’s date to the estimated lambing 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 + 17 days, one estrous cycle later.",
      "format": "date"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "d": "2026-08-04",
      "on": "2026-10-03"
    },
    "outputs": {
      "due": "2026-12-30",
      "earliest": "2026-12-26",
      "latest": "2027-01-03",
      "days": 60,
      "left": 88,
      "stage": "Day 60 of about 148: 88 days to the estimated lambing date.",
      "heat": "2026-08-21"
    },
    "text": "Your ewe is due to lamb about December 30, 2026, between December 26, 2026 and January 3, 2027."
  },
  "examples": [
    {
      "given": {
        "d": "2026-04-01",
        "on": "2026-06-01"
      },
      "expect": {
        "due": "2026-08-27",
        "earliest": "2026-08-23",
        "latest": "2026-08-31",
        "days": 61,
        "left": 87,
        "heat": "2026-04-18",
        "stage": "Day 61 of about 148: 87 days to the estimated lambing date."
      },
      "source": "Alabama Cooperative Extension System, Reproductive Management: Dairy Goats and Sheep (Table 3: numbers based on a 148-day gestation period), https://www.aces.edu/blog/topics/sheep-goats/reproductive-management-dairy-goats-and-sheep/ (retrieved 2026-10-03); University of Missouri Extension, Breeding Season Considerations for Sheep and Goats, G2611 (the gestation period ranges between 144 and 152 days), https://extension.missouri.edu/publications/g2611 (retrieved 2026-10-03); Merck Veterinary Manual, Reproductive Physiology of Sheep (in ewes, estrous cycles average 16 to 17 days), https://www.merckvetmanual.com/management-and-nutrition/management-of-reproduction-sheep/reproductive-physiology-of-sheep (retrieved 2026-10-03); hand calculation in content.mdx: 1 April 2026 + 144, 148 and 152 days"
    },
    {
      "given": {
        "d": "2027-11-01",
        "on": "2028-03-30"
      },
      "expect": {
        "due": "2028-03-28",
        "earliest": "2028-03-24",
        "latest": "2028-04-01",
        "days": 150,
        "left": -2
      },
      "source": "Alabama Cooperative Extension System, Reproductive Management: Dairy Goats and Sheep (Table 3: numbers based on a 148-day gestation period), https://www.aces.edu/blog/topics/sheep-goats/reproductive-management-dairy-goats-and-sheep/ (retrieved 2026-10-03); University of Missouri Extension, Breeding Season Considerations for Sheep and Goats, G2611 (the gestation period ranges between 144 and 152 days), https://extension.missouri.edu/publications/g2611 (retrieved 2026-10-03); hand calculation in content.mdx (2028 is a leap year)"
    }
  ],
  "sources": [
    "University of Missouri Extension, Breeding Season Considerations for Sheep and Goats, G2611 (the gestation period ranges between 144 and 152 days; October 2023). https://extension.missouri.edu/publications/g2611 (retrieved 2026-10-03)",
    "Alabama Cooperative Extension System, Reproductive Management: Dairy Goats and Sheep (Table 3: numbers based on a 148-day gestation period; August 2019). https://www.aces.edu/blog/topics/sheep-goats/reproductive-management-dairy-goats-and-sheep/ (retrieved 2026-10-03)",
    "Merck Veterinary Manual, Reproductive Physiology of Sheep (in ewes, estrous cycles average 16 to 17 days; updated March 2026). https://www.merckvetmanual.com/management-and-nutrition/management-of-reproduction-sheep/reproductive-physiology-of-sheep (retrieved 2026-10-03)"
  ],
  "related": [
    "goat-gestation",
    "mare-gestation",
    "dog-pregnancy",
    "date"
  ],
  "changelog": []
}