{
    "name": "Pregnancy Calculator",
    "url": "https://calculators.geekmidst.com/calculators/pregnancy-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/pregnancy-calculator.md",
    "category": "Health & fitness",
    "description": "Find how many weeks and days pregnant you are on any date from the first day of your last period, with trimester, due date and key milestone dates.",
    "summary": "Pregnancy is counted from the first day of your last menstrual period (LMP), about two weeks before conception. The due date is 280 days (40 weeks) after that day.",
    "also_called": [
        "Pregnancy week calculator",
        "Gestational age 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": "lmp",
            "label": "First day of last period",
            "type": "date",
            "default": "2026-05-01"
        },
        {
            "name": "cycle",
            "label": "Usual cycle length",
            "type": "number",
            "default": "28",
            "unit": "days",
            "optional": true
        },
        {
            "name": "as_of",
            "label": "Calculate for date",
            "type": "date",
            "default": "",
            "optional": true
        }
    ],
    "outputs": [
        {
            "key": "gestational_age",
            "label": "You are",
            "format": "text"
        },
        {
            "key": "trimester",
            "label": "Trimester",
            "format": "text"
        },
        {
            "key": "due_date",
            "label": "Estimated due date",
            "format": "text"
        },
        {
            "key": "days_left",
            "label": "Days until due date",
            "format": "integer"
        },
        {
            "key": "progress",
            "label": "Progress through 40 weeks",
            "format": "percent"
        },
        {
            "key": "conception",
            "label": "Estimated conception",
            "format": "text"
        }
    ],
    "formula": {
        "text": "Start = LMP + (cycle length − 28) days;  Gestational age = date − start;  Due date = start + 280 days",
        "variables": {
            "LMP": "first day of the last menstrual period",
            "cycle length": "days from one period to the next (28 if unknown)"
        }
    },
    "worked_example": {
        "inputs": {
            "lmp": "2026-03-01",
            "cycle": "28",
            "as_of": "2026-09-15"
        },
        "steps": [
            "From 1 March to 15 September 2026 is 198 days.",
            "198 days = 28 weeks and 2 days, which is in the third trimester (from 28 weeks).",
            "Due date = 1 March 2026 + 280 days = 6 December 2026, 82 days after 15 September."
        ],
        "result": "With a last period starting 1 March 2026, on 15 September 2026 you are 28 weeks and 2 days pregnant, with an estimated due date of 6 December 2026."
    },
    "interpretation": "The due date is an estimate: relatively few babies arrive on the day itself, and birth from 37 weeks onward is considered term. If you have had a dating ultrasound, the scan-based dates in your notes take priority over this calculation.",
    "assumptions": [
        "Pregnancy dated from the LMP by convention: due date = LMP + 280 days (ACOG).",
        "Longer or shorter cycles shift the dates by (cycle − 28) days, assuming ovulation 14 days before the next period.",
        "Trimesters: first to 13 weeks 6 days, second 14 weeks to 27 weeks 6 days, third from 28 weeks."
    ],
    "limitations": [
        "Irregular cycles, recent hormonal contraception or an uncertain LMP make date-based estimates unreliable.",
        "A first-trimester ultrasound is the most accurate way to date a pregnancy."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why am I “2 weeks pregnant” at conception?",
            "answer": "Pregnancy weeks are counted from the first day of your last period, not from conception, so the first two weeks happen before you conceive."
        },
        {
            "question": "My scan gave a different due date. Which is right?",
            "answer": "Use the scan date. ACOG advises changing the due date to the ultrasound estimate when the difference is larger than a set threshold (for example, more than 7 days at 9–13 weeks)."
        }
    ],
    "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": "Due Date Calculator",
            "url": "https://calculators.geekmidst.com/calculators/due-date-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"
}