{
  "id": "pregnancy",
  "version": "89983ae0475a",
  "status": "published",
  "name": "Pregnancy Calculator",
  "question": "How far along is my pregnancy?",
  "summary": "Works out how many weeks and days pregnant you are on a date, the trimester, the due date and milestone dates, from the last period, the due date, an ultrasound or the conception date.",
  "category": "health",
  "subcategory": "pregnancy",
  "url": "https://www.acalculator.org/health/pregnancy-calculator",
  "markdown": "https://www.acalculator.org/health/pregnancy-calculator.md",
  "kind": "function",
  "method": "Weeks pregnant = (date − start) ÷ 7, where the start is the first day of the last period + (cycle length − 28) days, the due date − 280 days, the ultrasound date − the gestational age it gave, or the conception date − 14 days.",
  "assumptions": [
    "A pregnancy is counted from the first day of the last period and lasts 280 days (40 weeks) to the due date (ACOG).",
    "Ovulation and conception happen 14 days before the next period would start, so a cycle longer or shorter than 28 days moves the dates by the difference.",
    "Trimesters: first to 13 weeks 6 days, second from 14 weeks 0 days, third from 28 weeks 0 days. Full term starts at 39 weeks 0 days.",
    "Before the start, or more than 44 weeks after it, how far along is left out and a note says so.",
    "An estimate, not medical advice: a first-trimester ultrasound is the most accurate way to date a pregnancy."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "method": {
        "title": "Based on",
        "description": "What you know: the first day of your last period, the conception date, an ultrasound, or the due date.",
        "type": "string",
        "enum": [
          "lmp",
          "due",
          "ultrasound",
          "conception"
        ]
      },
      "lmp": {
        "title": "First day of your last period",
        "description": "The first day of your last menstrual period.",
        "type": "string",
        "format": "date"
      },
      "cycle": {
        "title": "Cycle length (days)",
        "description": "Days from the first day of one period to the first day of the next. 28 if you are not sure.",
        "type": "integer",
        "minimum": 21,
        "maximum": 45
      },
      "conception": {
        "title": "Date of conception",
        "description": "The day you conceived.",
        "type": "string",
        "format": "date"
      },
      "scan": {
        "title": "Ultrasound date",
        "description": "The day of the ultrasound scan.",
        "type": "string",
        "format": "date"
      },
      "scanWeeks": {
        "title": "Weeks at the scan",
        "description": "The gestational age the scan gave: whole weeks.",
        "type": "integer",
        "minimum": 4,
        "maximum": 42
      },
      "scanDays": {
        "title": "And days",
        "description": "The gestational age the scan gave: days past the whole weeks, 0 to 6.",
        "type": "integer",
        "minimum": 0,
        "maximum": 6
      },
      "due": {
        "title": "Your due date",
        "description": "The estimated due date you were given.",
        "type": "string",
        "format": "date"
      },
      "on": {
        "title": "Work out on",
        "description": "The date to work out how far along the pregnancy is. Today, unless you change it.",
        "type": "string",
        "format": "date"
      }
    }
  },
  "outputs": {
    "ga": {
      "label": "How far along",
      "description": "Weeks and days of pregnancy on the work-out date, counted from the start.",
      "format": "duration"
    },
    "stage": {
      "label": "Stage",
      "description": "The trimester on the work-out date, or a note when the date is outside the pregnancy.",
      "format": "text"
    },
    "due": {
      "label": "Estimated due date",
      "description": "The estimated due date: 280 days (40 weeks) after the start.",
      "format": "date"
    },
    "daysLeft": {
      "label": "Days until the due date",
      "description": "Days from the work-out date to the due date.",
      "format": "integer"
    },
    "done": {
      "label": "Share of 40 weeks",
      "description": "How much of the 280 days to the due date has passed.",
      "format": "percent"
    },
    "start": {
      "label": "Pregnancy counted from",
      "description": "Day 0 of the count: the first day of the last period, adjusted for cycle length.",
      "format": "date"
    },
    "conception": {
      "label": "Likely conception date",
      "description": "About 14 days after the start, or the conception date you gave.",
      "format": "date"
    },
    "second": {
      "label": "Second trimester starts",
      "description": "The first day of the second trimester: 14 weeks 0 days.",
      "format": "date"
    },
    "third": {
      "label": "Third trimester starts",
      "description": "The first day of the third trimester: 28 weeks 0 days.",
      "format": "date"
    },
    "fullTerm": {
      "label": "Full term from",
      "description": "The start of full term: 39 weeks 0 days (ACOG).",
      "format": "date"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "method": "lmp",
      "lmp": "2026-07-07",
      "cycle": 28,
      "conception": "2026-08-18",
      "scan": "2026-09-22",
      "scanWeeks": 12,
      "scanDays": 0,
      "due": "2027-05-11",
      "on": "2026-09-29"
    },
    "outputs": {
      "ga": {
        "weeks": 12,
        "days": 0
      },
      "stage": "First trimester",
      "due": "2027-04-13",
      "daysLeft": 196,
      "done": 30,
      "start": "2026-07-07",
      "conception": "2026-07-21",
      "second": "2026-10-13",
      "third": "2027-01-19",
      "fullTerm": "2027-04-06"
    },
    "text": "On September 29, 2026 you are 12 weeks pregnant (First trimester). Estimated due date: April 13, 2027."
  },
  "examples": [
    {
      "given": {
        "method": "lmp",
        "lmp": "2026-06-01",
        "cycle": 28,
        "on": "2026-09-27"
      },
      "expect": {
        "ga": {
          "weeks": 16,
          "days": 6
        },
        "stage": "Second trimester",
        "due": "2027-03-08",
        "daysLeft": 162,
        "done": 42.142857142857146,
        "second": "2026-09-07",
        "third": "2026-12-14",
        "fullTerm": "2027-03-01"
      },
      "source": "ACOG Committee Opinion 700 (LMP + 280 days) and trimester limits; hand calculation in content.mdx"
    },
    {
      "given": {
        "method": "due",
        "due": "2026-12-25",
        "on": "2026-09-27"
      },
      "expect": {
        "start": "2026-03-20",
        "ga": {
          "weeks": 27,
          "days": 2
        },
        "stage": "Second trimester",
        "daysLeft": 89
      },
      "source": "ACOG CO 700 (due date = start + 280 days); hand calculation in content.mdx"
    },
    {
      "given": {
        "method": "conception",
        "conception": "2026-02-14",
        "on": "2026-09-27"
      },
      "expect": {
        "ga": {
          "weeks": 34,
          "days": 1
        },
        "stage": "Third trimester",
        "due": "2026-11-07",
        "daysLeft": 41
      },
      "source": "ACOG CO 700 (conception about day 14); hand calculation in content.mdx"
    },
    {
      "given": {
        "method": "ultrasound",
        "scan": "2026-07-01",
        "scanWeeks": 8,
        "scanDays": 2,
        "on": "2026-09-27"
      },
      "expect": {
        "start": "2026-05-04",
        "ga": {
          "weeks": 20,
          "days": 6
        },
        "due": "2027-02-08"
      },
      "source": "ACOG CO 700 (dating by ultrasound); hand calculation in content.mdx"
    }
  ],
  "sources": [
    "American College of Obstetricians and Gynecologists. Committee Opinion No. 700: Methods for Estimating the Due Date. Obstet Gynecol. 2017;129(5):e150-e154. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date",
    "American College of Obstetricians and Gynecologists. Committee Opinion No. 579: Definition of Term Pregnancy. Obstet Gynecol. 2013;122(5):1139-1140. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2013/11/definition-of-term-pregnancy",
    "Bull JR, Rowland SP, Scherwitzl EB, Scherwitzl R, Danielsson KG, Harper J. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. NPJ Digit Med. 2019;2:83. https://pmc.ncbi.nlm.nih.gov/articles/PMC6710244/"
  ],
  "related": [
    "due-date",
    "ovulation"
  ],
  "changelog": [
    {
      "date": "2026-09-28",
      "note": "The date boxes are labelled Date of conception and Your due date, apart from the Based on choices."
    }
  ]
}