Corrected QT Interval (QTc)
Corrects the QT interval for heart rate extremes (choose from Bazett, Fridericia, Framingham, Hodges, or Rautaharju formulas).
Interpreting the QT interval on any ECG: the QT normally shortens as heart rate rises, so it must be corrected before comparison with normal values. Essential before and during treatment with QT-prolonging drugs, in electrolyte disturbance, and when congenital long-QT syndrome is suspected.
An uncorrected QT cannot be interpreted. Correction standardises the interval to a heart rate of 60 bpm, allowing comparison against validated thresholds and detection of clinically important prolongation.
Advice
Enter values above to calculate the corrected QT interval.
Ensure the QT interval measurement does not mistakenly include a U wave. If it does, re-measure, recalculate, and consider potential etiologies of U waves.
If there is no U wave, consider common causes of a prolonged QT interval, including:
- Electrolyte abnormalities.
- Intrinsic cardiac causes.
- Central causes.
- Medications.
If a short QT interval is observed, confirm measurement accuracy and consider short QT syndrome.
Formula
RR interval = 60 / HR
Bazett Formula: QTc = QT interval / √(RR interval)
Fridericia Formula: QTc = QT interval / (RR interval)1/3
Framingham Formula: QTc = QT interval + 154 × (1 - RR interval)
Hodges Formula: QTc = QT interval + 1.75 × [(60 / RR interval) - 60]
Rautaharju Formula: QTc = QT interval × (120 + HR) / 180
QT in milliseconds, RR in seconds, HR in beats per minute. All formulas are anchored so QTc = QT at 60 bpm.
About this tool
This calculator implements the five standard heart-rate corrections of the QT interval. Bazett remains the most widely used and is the basis of most guidelines and ECG machine readings, but it overcorrects at high heart rates and undercorrects at low ones. Above 90 or below 60 bpm, confirm with Fridericia or a linear formula such as Framingham or Hodges. In atrial fibrillation or an irregular rhythm, average QT and RR over at least 5-10 beats before applying any formula.