{
    "name": "Due Date Calculator",
    "url": "https://calculators.geekmidst.com/calculators/due-date-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/due-date-calculator.md",
    "category": "Health & fitness",
    "description": "Estimate your due date from your last period, a known conception date, a day-3 or day-5 IVF embryo transfer, or an ultrasound scan, using ACOG conventions.",
    "summary": "A due date is 280 days after the first day of the last period, 266 days after conception, or 261 or 263 days after a day-5 or day-3 IVF embryo transfer.",
    "also_called": [
        "EDD calculator",
        "Pregnancy due date calculator",
        "IVF due date calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "method",
            "label": "Calculate from",
            "type": "select",
            "default": "lmp",
            "options": {
                "lmp": "First day of last period",
                "conception": "Conception date",
                "ivf": "IVF embryo transfer",
                "ultrasound": "Ultrasound scan"
            }
        },
        {
            "name": "lmp",
            "label": "First day of last period",
            "type": "date",
            "default": "2026-05-01",
            "shown_when": {
                "method": "lmp"
            }
        },
        {
            "name": "cycle",
            "label": "Usual cycle length",
            "type": "number",
            "default": "28",
            "unit": "days",
            "optional": true,
            "shown_when": {
                "method": "lmp"
            }
        },
        {
            "name": "conception_date",
            "label": "Conception date",
            "type": "date",
            "default": "2026-05-15",
            "shown_when": {
                "method": "conception"
            }
        },
        {
            "name": "transfer_date",
            "label": "Embryo transfer date",
            "type": "date",
            "default": "2026-05-20",
            "shown_when": {
                "method": "ivf"
            }
        },
        {
            "name": "embryo_day",
            "label": "Embryo age at transfer",
            "type": "segmented",
            "default": "5",
            "options": {
                "5": "Day 5 (blastocyst)",
                "3": "Day 3"
            },
            "shown_when": {
                "method": "ivf"
            }
        },
        {
            "name": "scan_date",
            "label": "Scan date",
            "type": "date",
            "default": "2026-07-01",
            "shown_when": {
                "method": "ultrasound"
            }
        },
        {
            "name": "scan_weeks",
            "label": "Gestational age at scan (weeks)",
            "type": "number",
            "default": "12",
            "unit": "weeks",
            "shown_when": {
                "method": "ultrasound"
            }
        },
        {
            "name": "scan_days",
            "label": "Plus days",
            "type": "number",
            "default": "0",
            "unit": "days",
            "optional": true,
            "shown_when": {
                "method": "ultrasound"
            }
        }
    ],
    "outputs": [
        {
            "key": "due_date",
            "label": "Estimated due date",
            "format": "text"
        },
        {
            "key": "term_window",
            "label": "Term window (37 weeks to 41 weeks 6 days)",
            "format": "text"
        },
        {
            "key": "lmp_equivalent",
            "label": "Pregnancy dated from (LMP equivalent)",
            "format": "text"
        },
        {
            "key": "conception",
            "label": "Estimated conception",
            "format": "text"
        }
    ],
    "formula": {
        "text": "LMP: due = LMP + (cycle − 28) + 280;  Conception: due = conception + 266;  IVF day 5: transfer + 261;  IVF day 3: transfer + 263;  Scan: due = scan date + 280 − gestational age at scan (days)",
        "variables": {
            "LMP": "first day of last period",
            "280 days": "40 weeks",
            "gestational age at scan": "weeks × 7 + days, as measured by ultrasound"
        }
    },
    "worked_example": {
        "inputs": {
            "method": "lmp",
            "lmp": "2026-03-01",
            "cycle": "28",
            "conception_date": "2026-03-15",
            "transfer_date": "2026-03-20",
            "embryo_day": "5",
            "scan_date": "2026-06-01",
            "scan_weeks": "12",
            "scan_days": "3"
        },
        "steps": [
            "Last period started 1 March 2026 and the cycle is 28 days, so no adjustment is needed.",
            "Due date = 1 March 2026 + 280 days = 6 December 2026.",
            "Term runs from 37 weeks (+259 days, 15 November) to 41 weeks 6 days (+293 days, 19 December)."
        ],
        "result": "A last period starting on 1 March 2026 gives an estimated due date of Sunday 6 December 2026."
    },
    "interpretation": "IVF dates are the most precise because the embryo’s age is known. Otherwise, a first-trimester scan is more accurate than period dates, and your care team will normally use it to confirm or change the due date.",
    "assumptions": [
        "Conventions from ACOG Committee Opinion 700: 280 days from LMP; 261 days from a day-5 and 263 days from a day-3 embryo transfer.",
        "Conception taken as 14 days after the (cycle-adjusted) LMP, 266 days before the due date."
    ],
    "limitations": [
        "Period-based dates assume regular cycles with ovulation 14 days before the next period.",
        "The scan method assumes the gestational age you enter is the one reported on your scan."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "What is Naegele’s rule?",
            "answer": "It is a shortcut for the same calculation: take the first day of the last period, subtract three months and add seven days (and a year where needed)."
        },
        {
            "question": "Why does a day-5 transfer use 261 days?",
            "answer": "A day-5 embryo is already 5 days past fertilisation, and fertilisation corresponds to 2 weeks of gestational age, so 280 − 14 − 5 = 261 days remain."
        }
    ],
    "sources": [
        {
            "title": "ACOG Committee Opinion 700: Methods for Estimating the Due Date (2017)",
            "url": "https://www.healthcare.uiowa.edu/familymedicine/fpinfo/OB/OB2017/ACOG%20redating%20gestational%20age.pdf"
        },
        {
            "title": "StatPearls: Estimated Date of Delivery",
            "url": "https://www.statpearls.com/ArticleLibrary/viewarticle/21375"
        }
    ],
    "related": [
        {
            "name": "Pregnancy Calculator",
            "url": "https://calculators.geekmidst.com/calculators/pregnancy-calculator"
        },
        {
            "name": "Pregnancy Conception Calculator",
            "url": "https://calculators.geekmidst.com/calculators/pregnancy-conception-calculator"
        },
        {
            "name": "Pregnancy Weight Gain Calculator",
            "url": "https://calculators.geekmidst.com/calculators/pregnancy-weight-gain-calculator"
        },
        {
            "name": "Date Difference Calculator",
            "url": "https://calculators.geekmidst.com/calculators/date-difference-calculator"
        }
    ],
    "disclaimer": "This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.",
    "publisher": "GM¹X CalcVerse"
}