QTc Calculator
What is QTc Calculator
The corrected QT interval (QTc) adjusts the measured QT for heart rate so it can be compared across different rates. This calculator uses the Bazett formula, QTc = QT divided by the square root of the RR interval, and also shows the Fridericia, Framingham, and Hodges corrections. A prolonged QTc raises the risk of dangerous arrhythmias such as torsades de pointes.
How to use
- Enter the measured QT interval in milliseconds.
- Enter the heart rate in beats per minute.
- Select the patient's sex, since the thresholds differ.
- Read the Bazett QTc and its interpretation, plus the other formulas.
When to use it
Have a QT of 400 ms at a heart rate of 75? Enter both and you get a Bazett QTc of 447 ms, borderline for a man and normal for a woman. Bazett tends to over-correct at fast rates, so the Fridericia value shown alongside (431 ms) is a useful cross-check.
Frequently asked questions
What is the Bazett formula for QTc?
QTc = QT ÷ √RR, where RR is the interval between beats in seconds (RR = 60 ÷ heart rate). For QT 400 ms at 75 bpm, RR is 0.8 s and QTc is 400 ÷ √0.8 = about 447 ms.
Why correct the QT for heart rate?
The QT interval naturally shortens as the heart speeds up and lengthens as it slows. Correcting to a standard rate lets you compare the QT over time and between patients, and judge whether it is truly prolonged.
What QTc counts as prolonged?
Commonly, a QTc above 450 ms in men and above 470 ms in women is considered prolonged, with a borderline zone just below. A QTc of 500 ms or more is markedly prolonged and warrants particular caution.
Can I share this tool with my inputs pre-filled?
Yes. The URL updates automatically as you type. Copy it from the address bar or use the Share button — anyone who opens the link will see your exact inputs ready to go.
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