{
  "slug": "due-date",
  "title": "Pregnancy Due Date Calculator",
  "heading": "Pregnancy Due Date Calculator",
  "category": "fitness-health",
  "url": "https://www.revenuelab.fyi/toolbox/due-date",
  "summary": "Estimated due date, trimesters, and weeks along.",
  "description": "Naegele's rule adds 280 days to the first day of the last menstrual period. Only about 4% of babies arrive on the estimated date; the 37–42 week window is the realistic range.",
  "formula": "Due date = Last period + 280 days (adjusted for cycle length).",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=due-date",
  "inputs": [
    {
      "id": "lmp",
      "label": "First day of last period",
      "kind": "date",
      "hint": null,
      "default": "2026-04-01"
    },
    {
      "id": "cycle",
      "label": "Average cycle length",
      "kind": "number",
      "hint": null,
      "default": 28,
      "unit": "days",
      "min": 20,
      "max": 45
    }
  ],
  "outputs": [
    {
      "id": "due",
      "label": "Estimated due date",
      "format": "raw",
      "hint": null,
      "primary": true
    },
    {
      "id": "weeks",
      "label": "How far along today",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "trimester",
      "label": "Current trimester",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "daysLeft",
      "label": "Days remaining",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "conception",
      "label": "Estimated conception date",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "viability",
      "label": "24-week viability milestone",
      "format": "raw",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "First day of last period: 2026-04-01",
      "Average cycle length: 28 days"
    ],
    "outputs": [
      "Estimated due date: January 6, 2027",
      "How far along today: 26w 0d",
      "Current trimester: Second",
      "Days remaining: 98",
      "Estimated conception date: April 15, 2026",
      "24-week viability milestone: September 16, 2026"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter first day of last period.",
      "Enter average cycle length (days).",
      "Read your estimated due date on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "lmp": "2026-04-01",
        "cycle": 20
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "lmp": "2026-04-01",
        "cycle": 28
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "lmp": "2026-04-01",
        "cycle": 45
      }
    }
  ],
  "limitations": [
    "Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.",
    "Results do not account for medical conditions, medication, or pregnancy.",
    "Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it."
  ],
  "faq": [
    {
      "q": "How does the pregnancy due date calculator work?",
      "a": "Naegele's rule adds 280 days to the first day of the last menstrual period. Only about 4% of babies arrive on the estimated date; the 37–42 week window is the realistic range. The underlying maths is: Due date = Last period + 280 days (adjusted for cycle length)."
    },
    {
      "q": "What do I need to enter?",
      "a": "2 values: first day of last period, and average cycle length. Each field starts with a sensible default, so you can change one number at a time and watch the result move."
    },
    {
      "q": "What does the estimated due date result mean?",
      "a": "It is returned as a plain value and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds."
    },
    {
      "q": "Is this calculator free, and do I need an account?",
      "a": "Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser."
    },
    {
      "q": "How accurate is the result?",
      "a": "It applies the standard formula exactly, so the arithmetic is precise. Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass."
    },
    {
      "q": "Who is this tool for?",
      "a": "It's built for anyone tracking a health or training target and wanting the standard formula applied correctly, without a signup or an app."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/age-calculator",
    "https://www.revenuelab.fyi/toolbox/ideal-weight"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Pregnancy Due Date Calculator (https://www.revenuelab.fyi/toolbox/due-date)"
}