Corrected QT (QTc) Bazett Calculator

Enter your patient's QT interval (in milliseconds) and heart rate (in bpm) to calculate the corrected QT interval (QTc) using Bazett's formula. The tool returns the QTc value and flags whether it falls within normal, borderline, or prolonged ranges — helping you quickly assess cardiac risk at the bedside.

Disclaimer: This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions.

ms

Measured QT interval from the ECG (in milliseconds)

bpm

Patient's heart rate in beats per minute

Results

QTc (Bazett)

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RR Interval

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Interpretation

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QTc Status

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Frequently Asked Questions

What is the Bazett formula for QTc?

Bazett's formula calculates the corrected QT interval as QTc = QT / √RR, where QT is the measured QT interval in seconds and RR is the RR interval in seconds (60 / heart rate). It is the most widely used formula in clinical practice, though it can overcorrect at very high or very low heart rates.

How do I calculate QTc using Bazett's formula?

First, measure the QT interval from the ECG in milliseconds. Then calculate the RR interval by dividing 60 by the heart rate (in seconds). Finally, divide the QT interval by the square root of the RR interval. For example, a QT of 400 ms at 75 bpm gives an RR of 0.8 s and a QTc of 400 / √0.8 ≈ 447 ms.

What is a normal QTc interval?

A normal QTc is generally below 440 ms in men and below 460 ms in women. Values between 440–470 ms (men) or 460–480 ms (women) are considered borderline. A QTc above 500 ms is associated with a significantly increased risk of serious arrhythmias, including Torsades de Pointes.

What is QTc prolongation and why does it matter?

QTc prolongation refers to an abnormally long corrected QT interval on the ECG, indicating delayed cardiac repolarization. It increases the risk of life-threatening arrhythmias such as Torsades de Pointes and sudden cardiac death. It can be caused by medications, electrolyte imbalances, congenital conditions, or underlying heart disease.

What is my QTc if my QT interval is 360 ms and heart rate is 60 bpm?

At a heart rate of 60 bpm, the RR interval is exactly 1.0 second. Using Bazett's formula, QTc = 360 / √1.0 = 360 ms. At a heart rate of exactly 60 bpm, the QTc equals the raw QT interval, since the RR interval normalizes to 1 second.

Are there other QTc correction formulas besides Bazett?

Yes. Fridericia's formula uses the cube root of RR (QTc = QT / ∛RR), which performs better at extreme heart rates. The Framingham formula (QTc = QT + 0.154 × (1 − RR)) and Hodges formula (QTc = QT + 1.75 × (HR − 60)) are also used. Bazett's formula remains the most common in clinical settings despite its limitations.

Which drugs can prolong the QT interval?

Many commonly prescribed medications can prolong the QT interval, including certain antibiotics (e.g., azithromycin, fluoroquinolones), antiarrhythmics (e.g., amiodarone, sotalol), antipsychotics (e.g., haloperidol, quetiapine), and antidepressants. Checking crediblemeds.org or similar resources before prescribing in patients with already prolonged QTc is strongly recommended.

Can electrolyte imbalances affect the QTc interval?

Yes. Hypokalemia, hypomagnesemia, and hypocalcemia are all associated with QT prolongation. Correcting these electrolyte abnormalities is an important step in managing patients with prolonged QTc, especially before or alongside other treatments.