{
  "id": "qtc",
  "version": "38b4e5905a5f",
  "status": "published",
  "name": "QTc Calculator",
  "question": "What is the QTc?",
  "summary": "Corrects the QT interval of an ECG for heart rate with the Bazett, Fridericia, Framingham, and Hodges formulas, and reads the result with the AHA/ACCF/HRS cut-offs for men and women.",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/qtc-calculator",
  "markdown": "https://www.acalculator.org/health/qtc-calculator.md",
  "kind": "function",
  "method": "RR (s) = 60 ÷ heart rate. Bazett: QT ÷ √RR. Fridericia: QT ÷ ∛RR. Framingham: QT + 154 × (1 − RR). Hodges: QT + 1.75 × (heart rate − 60). QT in ms.",
  "assumptions": [
    "A regular rhythm; each QTc is rounded to a whole millisecond and the reading uses the headline value.",
    "Long QTc: 450 ms or more in men, 460 ms or more in women; short: 390 ms or less (AHA/ACCF/HRS 2009). Over 500 ms is shown separately (Drew 2010, AHA/ACCF statement on torsade de pointes: highly abnormal)."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "qt": {
        "title": "QT interval (ms)",
        "description": "The measured QT interval on the ECG, in milliseconds.",
        "type": "number",
        "minimum": 200,
        "maximum": 700
      },
      "mode": {
        "title": "Rate given as",
        "description": "Enter the heart rate in beats per minute, or the RR interval in milliseconds.",
        "type": "string",
        "enum": [
          "hr",
          "rr"
        ]
      },
      "hr": {
        "title": "Heart rate (beats/min)",
        "description": "Heart rate at the time of the ECG, in beats per minute.",
        "type": "number",
        "minimum": 30,
        "maximum": 250
      },
      "rr": {
        "title": "RR interval (ms)",
        "description": "Time between two R waves, in milliseconds.",
        "type": "number",
        "minimum": 240,
        "maximum": 2000
      },
      "formula": {
        "title": "Headline formula",
        "description": "Which formula the headline shows. The page shows all four.",
        "type": "string",
        "enum": [
          "bazett",
          "fridericia",
          "framingham",
          "hodges"
        ]
      },
      "sex": {
        "title": "Sex",
        "description": "Sex at birth. The long-QTc cut-off is 450 ms for men and 460 ms for women.",
        "type": "string",
        "enum": [
          "male",
          "female"
        ]
      }
    }
  },
  "outputs": {
    "qtc": {
      "label": "QTc",
      "description": "The corrected QT by the headline formula, in ms.",
      "format": "integer"
    },
    "reading": {
      "label": "Reading",
      "description": "Short, normal, or long QTc for the sex.",
      "format": "text"
    },
    "bazett": {
      "label": "Bazett",
      "description": "QT ÷ √RR, in ms.",
      "format": "integer"
    },
    "fridericia": {
      "label": "Fridericia",
      "description": "QT ÷ ∛RR, in ms.",
      "format": "integer"
    },
    "framingham": {
      "label": "Framingham",
      "description": "QT + 154 × (1 − RR), in ms.",
      "format": "integer"
    },
    "hodges": {
      "label": "Hodges",
      "description": "QT + 1.75 × (heart rate − 60), in ms.",
      "format": "integer"
    },
    "rate": {
      "label": "Heart rate",
      "description": "Heart rate in beats per minute.",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "qt": 400,
      "mode": "hr",
      "hr": 75,
      "rr": 800,
      "formula": "bazett",
      "sex": "male"
    },
    "outputs": {
      "qtc": 447,
      "reading": "Normal range",
      "bazett": 447,
      "fridericia": 431,
      "framingham": 431,
      "hodges": 426,
      "rate": 75
    },
    "text": "The Bazett QTc is 447 ms: Normal range."
  },
  "examples": [
    {
      "given": {
        "qt": 400,
        "mode": "hr",
        "hr": 75,
        "formula": "bazett",
        "sex": "male"
      },
      "expect": {
        "qtc": 447,
        "reading": "Normal range",
        "bazett": 447,
        "fridericia": 431,
        "framingham": 431,
        "hodges": 426
      },
      "source": "Bazett 1920: 400 ÷ √0.8 = 447.2; Fridericia 1920: 400 ÷ ∛0.8 = 430.9; Sagie 1992: 400 + 154 × 0.2 = 430.8; Hodges 1983: 400 + 1.75 × 15 = 426.25 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "qt": 400,
        "mode": "hr",
        "hr": 60,
        "formula": "fridericia",
        "sex": "female"
      },
      "expect": {
        "qtc": 400,
        "bazett": 400,
        "fridericia": 400,
        "framingham": 400,
        "hodges": 400
      },
      "source": "At 60 beats/min the RR is 1 s, and all four formulas return the measured QT (hand calculation)"
    },
    {
      "given": {
        "qt": 360,
        "mode": "rr",
        "rr": 600,
        "formula": "bazett",
        "sex": "female"
      },
      "expect": {
        "qtc": 465,
        "reading": "Long: 460 ms or more",
        "fridericia": 427,
        "framingham": 422,
        "hodges": 430
      },
      "source": "RR 0.6 s (100 beats/min): Bazett 360 ÷ √0.6 = 464.8; Fridericia 360 ÷ ∛0.6 = 426.9; Framingham 360 + 154 × 0.4 = 421.6; Hodges 360 + 1.75 × 40 = 430 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "qt": 480,
        "mode": "hr",
        "hr": 90,
        "formula": "hodges",
        "sex": "male"
      },
      "expect": {
        "qtc": 533,
        "reading": "Long: over 500 ms",
        "bazett": 588
      },
      "source": "Hodges 480 + 1.75 × 30 = 532.5, shown as 533; Bazett 480 ÷ √(60/90) = 587.9 (hand calculation)"
    }
  ],
  "sources": [
    "Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370.",
    "Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469-486. https://doi.org/10.1111/j.0954-6820.1920.tb18266.x",
    "Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol. 1992;70(7):797-801. https://doi.org/10.1016/0002-9149(92)90562-D",
    "Hodges M, Salerno D, Erlien D. Bazett's QT correction reviewed: evidence that a linear QT correction for heart rate is better. J Am Coll Cardiol. 1983;1:694 (abstract).",
    "Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241-e250. https://doi.org/10.1161/CIRCULATIONAHA.108.191096",
    "Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the AHA and ACCF. Circulation. 2010;121(8):1047-1060. https://doi.org/10.1161/CIRCULATIONAHA.109.192704"
  ],
  "related": [],
  "changelog": [
    {
      "date": "2026-09-29",
      "note": "The chart varies the QT, so it is right in RR interval mode too (muse review)."
    },
    {
      "date": "2026-09-29",
      "note": "Published after this site's editorial review against the cited sources (no clinician review); the page notice says so. The separate long reading is now over 500 ms (Drew 2010), not 500 ms or more."
    }
  ]
}