QTc Calculator - Corrected QT Interval (Bazett, Fridericia, Framingham, Hodges)
QTc Calculator
Corrected QT interval with four formulas
Four Formulas
Bazett, Fridericia, Framingham and Hodges side by side, so you can see how much they agree.
Rate or RR
Enter the heart rate or the RR interval measured on the ECG.
Sex-Specific Ranges
Prolonged is 450 ms or more in males and 460 ms or more in females.
Private
Calculated in your browser.
Why the QT Interval Is Corrected
The QT interval, from the start of the QRS complex to the end of the T wave, shortens as the heart beats faster, so it is corrected to a standard rate of 60 bpm before comparing it with normal values. Bazett's formula QT/√RR is the oldest and most familiar, but over-corrects at fast rates; Fridericia's QT/∛RR and the linear Framingham and Hodges formulas behave better away from 60 bpm. Example: QT 400 ms at 75 bpm (RR 800 ms) gives Bazett 447 ms and Fridericia 431 ms.
A prolonged QTc can be caused by medicines, low potassium or magnesium, and inherited long-QT syndromes, and a QTc of 500 ms or more is linked to a higher risk of a dangerous arrhythmia called torsades de pointes. Manual QT measurement varies between readers, and the end of the T wave can be hard to see. These numbers support, but never replace, a clinician's interpretation of the whole ECG.
Key Takeaways
- Prefer Fridericia: It is more accurate than Bazett at fast or slow rates.
- 500 ms matters: A QTc of 500 ms or more needs prompt medical review.
- Not a diagnosis: Use alongside the full ECG and clinical picture.