QTc Calculator (Corrected QT Interval)

Calculate corrected QT interval (QTc) using the Bazett formula, accounting for heart rate when assessing ECG QT intervals. Used in cardiology education and arrhythmia risk reference.

❤️ Clinical Reference📐 QTc = QT / √(RR interval)🏥 Health
Measured QT interval (ms)
Heart rate (bpm)
Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
QTc Calculator (Corrected QT Interval)—QTc = QT / √(RR interval)milliseconds

Step-by-Step Examples

Example 1
Normal QTc

QT=380ms measured, HR=70bpm.

  • RR interval = 60/70 = 0.857 sec
  • QTc = 380/√0.857 = 380/0.926 = 410ms
  • Within normal range
✓ QTc = 410ms (normal)
Example 2
Borderline at High Heart Rate

QT=350ms measured, HR=100bpm (tachycardia).

  • RR = 60/100 = 0.6 sec
  • QTc = 350/√0.6 = 350/0.775 = 452ms
  • Borderline prolonged despite shorter raw QT — correction reveals the true risk
✓ QTc = 452ms (borderline)
Example 3
Prolonged QTc

QT=460ms measured, HR=65bpm.

  • RR = 60/65 = 0.923 sec
  • QTc = 460/√0.923 = 460/0.961 = 479ms
  • Prolonged — would warrant clinical attention for arrhythmia risk
✓ QTc = 479ms (prolonged)

Real-World Applications

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Cardiology Education
QTc calculation is fundamental to understanding ECG interpretation and arrhythmia risk.
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Pharmacovigilance Reference
Many medications carry QT-prolongation warnings; QTc monitoring concepts are taught in pharmacy and medical education.
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Clinical Training
QTc calculation is a core skill taught in cardiology fellowships, nursing programs, and emergency medicine training.
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Drug Safety Research
QTc prolongation assessment is a standard component of cardiac safety evaluation in pharmaceutical research.

Common Mistakes to Avoid

⚠️
Using only one formula without considering alternatives

Bazett's formula tends to overcorrect at high heart rates. Fridericia and Framingham formulas are sometimes preferred clinically, especially outside normal heart rate ranges.

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Treating this as a diagnostic tool

ECG interpretation, including QTc assessment, requires professional clinical training and should never replace evaluation by a qualified healthcare provider with the actual ECG tracing.

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Ignoring that QTc varies with measurement technique

Manual QT measurement has inherent variability between observers — automated ECG machine readings and manual measurements can differ meaningfully.

Frequently Asked Questions

What is QTc and why is it corrected? ▾
QTc is the QT interval corrected for heart rate, since the raw QT interval naturally shortens as heart rate increases. Correction allows meaningful comparison across different heart rates.
What is considered a normal QTc? ▾
Generally under 440ms for men and under 460ms for women, though specific thresholds vary by reference source and clinical context.
Why does QT prolongation matter clinically? ▾
Prolonged QTc is associated with increased risk of a dangerous arrhythmia called Torsades de Pointes, which can potentially lead to sudden cardiac death in severe cases.
What causes QT prolongation? ▾
Many factors including certain medications (antiarrhythmics, some antibiotics, antipsychotics), electrolyte abnormalities (low potassium, magnesium), congenital long QT syndrome, and various cardiac conditions.
Is Bazett the best correction formula? ▾
Bazett is most commonly used but tends to overcorrect at fast heart rates and undercorrect at slow rates. Fridericia's formula is considered by some experts to be more accurate across a wider heart rate range.

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