QTc Calculator
Bazett, Fridericia, Framingham and Hodges corrections.
Measure QT manually when automated values are borderline, from the start of QRS to the end of the T wave using the tangent method, excluding U waves.
QTc (Fridericia)
421 ms
Within normal limits
Above 500 ms the risk of torsades de pointes rises sharply regardless of sex, and QT-prolonging drugs should be reviewed.
How the QTc Calculator works
The QT interval shortens as heart rate rises, so a raw measurement cannot be compared against a fixed threshold. Correction formulas normalise it to a rate of 60 bpm. Bazett is the most familiar and the least accurate at rate extremes, which matters because that is exactly when the answer is most consequential.
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
Which QTc formula should be used?
Bazett (QT ÷ √RR) is the historical default but over-corrects at high heart rates and under-corrects at low ones. Fridericia (QT ÷ RR^⅓) performs better outside the normal rate range and is preferred in drug safety studies. Reporting more than one is common practice.
What QTc is considered prolonged?
Above 450 ms in men and 460 ms in women. Above 500 ms is associated with a markedly increased risk of torsades de pointes regardless of sex, and usually prompts review of any QT-prolonging medication.
Why does QTc matter clinically?
A prolonged QT interval predisposes to torsades de pointes, a polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation. Many common drugs prolong it, so QTc is checked before and during treatment with them.
How should QT be measured on the ECG?
From the start of the QRS complex to the end of the T wave, usually in lead II or V5, using the tangent method where the T wave descent is extrapolated to the baseline. U waves are excluded. Manual measurement is recommended when automated values are borderline.
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