{
  "id": "hcg",
  "version": "7d5553d0639e",
  "status": "published",
  "name": "hCG Calculator",
  "question": "What is my hCG doubling time?",
  "summary": "Computes the hCG doubling time and percent rise between two blood tests, the rise scaled to 48 hours, and compares it with the smallest 2-day rise seen in ongoing pregnancies (Barnhart 2016).",
  "category": "health",
  "subcategory": "pregnancy",
  "url": "https://www.acalculator.org/health/hcg-calculator",
  "markdown": "https://www.acalculator.org/health/hcg-calculator.md",
  "kind": "function",
  "method": "Doubling time = hours × ln 2 ÷ ln(second ÷ first) (halving time when it falls: hours × ln 2 ÷ |ln(second ÷ first)|); change = (second ÷ first − 1) × 100; 48-hour change = ((second ÷ first)^(48 ÷ hours) − 1) × 100.",
  "assumptions": [
    "hCG changes at a steady exponential rate between the two tests.",
    "Barnhart 2016 studied 285 women with an ongoing intrauterine pregnancy who had bleeding or pain in the first trimester; its smallest 2-day rise is 49% for a first value below 1,500 mIU/mL, 40% from 1,500 to 3,000, and 33% above 3,000.",
    "This is information, not a diagnosis. A single slow rise does not rule out a healthy pregnancy, and a normal rise does not rule out an ectopic one."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "h1": {
        "title": "First hCG (mIU/mL)",
        "description": "The first blood hCG result, in mIU/mL (the same as IU/L).",
        "type": "number",
        "minimum": 1,
        "maximum": 1000000
      },
      "h2": {
        "title": "Second hCG (mIU/mL)",
        "description": "The later blood hCG result, from the same lab if you can.",
        "type": "number",
        "minimum": 1,
        "maximum": 1000000
      },
      "hours": {
        "title": "Hours between tests",
        "description": "How many hours passed between the two blood draws; 48 for two days.",
        "type": "number",
        "minimum": 1,
        "maximum": 720
      }
    }
  },
  "outputs": {
    "time": {
      "label": "Doubling time (hours)",
      "description": "Hours for hCG to double at this rate; when it falls, hours for it to halve.",
      "format": "number"
    },
    "trend": {
      "label": "Direction",
      "description": "Whether hCG rose (doubling time) or fell (halving time).",
      "format": "text"
    },
    "days": {
      "label": "Doubling time (days)",
      "description": "The same time in days.",
      "format": "number"
    },
    "change": {
      "label": "Change between tests",
      "description": "Second ÷ first − 1, in percent.",
      "format": "percent"
    },
    "rise48": {
      "label": "Change over 48 hours",
      "description": "The change scaled to exactly 48 hours, assuming a steady exponential rate.",
      "format": "percent"
    },
    "minimum": {
      "label": "Smallest 2-day rise in Barnhart 2016",
      "description": "The 1st-percentile 2-day rise in ongoing intrauterine pregnancies, by the first level.",
      "format": "percent"
    },
    "compare": {
      "label": "Compared with that rise",
      "description": "Whether the 48-hour change is at least that rise.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "h1": 1000,
      "h2": 1800,
      "hours": 48
    },
    "outputs": {
      "time": 56.60398007229004,
      "trend": "Rising: doubling time",
      "days": 2.3584991696787516,
      "change": 80,
      "rise48": 80,
      "minimum": 49,
      "compare": "At or above it"
    },
    "text": "From 1,000 to 1,800 mIU/mL in 48 hours: the doubling time is 56.6 hours, a 80% change over 48 hours."
  },
  "examples": [
    {
      "given": {
        "h1": 1000,
        "h2": 2000,
        "hours": 48
      },
      "expect": {
        "time": 48,
        "days": 2,
        "change": 100,
        "rise48": 100,
        "minimum": 49,
        "compare": "At or above it"
      },
      "source": "Barnhart KT et al., Differences in Serum Human Chorionic Gonadotropin Rise in Early Pregnancy by Race and Value at Presentation, Obstet Gynecol 2016;128(3):504-511, doi:10.1097/AOG.0000000000001568 (2-day minimal rise 49% below 1,500 mIU/mL). https://pubmed.ncbi.nlm.nih.gov/27500326/; hand calculation in content.mdx: 48 × ln 2 ÷ ln 2 = 48 h"
    },
    {
      "given": {
        "h1": 1000,
        "h2": 1800,
        "hours": 48
      },
      "expect": {
        "time": 56.60398007229004,
        "change": 80,
        "rise48": 80
      },
      "source": "Barnhart KT et al., Obstet Gynecol 2016;128(3):504-511, doi:10.1097/AOG.0000000000001568. https://pubmed.ncbi.nlm.nih.gov/27500326/; hand calculation in content.mdx: 48 × ln 2 ÷ ln 1.8 = 56.6 h"
    },
    {
      "given": {
        "h1": 2000,
        "h2": 2500,
        "hours": 72
      },
      "expect": {
        "change": 25,
        "rise48": 16.039720840319475,
        "minimum": 40,
        "compare": "Below it",
        "time": 223.65242780438805
      },
      "source": "Barnhart KT et al., Obstet Gynecol 2016;128(3):504-511, doi:10.1097/AOG.0000000000001568 (2-day minimal rise 40% for 1,500 to 3,000 mIU/mL). https://pubmed.ncbi.nlm.nih.gov/27500326/; hand calculation in content.mdx: 1.25^(48/72) − 1 = 16.0%"
    },
    {
      "given": {
        "h1": 5000,
        "h2": 2500,
        "hours": 48
      },
      "expect": {
        "time": 48,
        "change": -50,
        "trend": "Falling: halving time",
        "minimum": 33,
        "compare": "Below it"
      },
      "source": "Barnhart KT et al., Obstet Gynecol 2016;128(3):504-511, doi:10.1097/AOG.0000000000001568 (2-day minimal rise 33% above 3,000 mIU/mL). https://pubmed.ncbi.nlm.nih.gov/27500326/; hand calculation in content.mdx: 48 × ln 2 ÷ |ln 0.5| = 48 h halving time"
    }
  ],
  "sources": [
    "Barnhart KT, Guo W, Cary MS, Morse CB, Chung K, Takacs P, Senapati S, Sammel MD. Differences in Serum Human Chorionic Gonadotropin Rise in Early Pregnancy by Race and Value at Presentation. Obstet Gynecol. 2016;128(3):504-511. doi:10.1097/AOG.0000000000001568. https://pubmed.ncbi.nlm.nih.gov/27500326/ (abstract read 2026-10-01)"
  ],
  "related": [
    "pregnancy",
    "due-date",
    "pregnancy-test"
  ],
  "changelog": []
}