Corrected QT (QTc) Calculator

How it is calculated

Enter the measured QT interval in milliseconds and the heart rate in beats per minute. The tool first finds the RR interval, RR = 60 ÷ HR (seconds between beats), then applies Bazett's correction, QTc = QT ÷ √RR. The corrected value is displayed in ms with one decimal, and the RR interval in seconds with two.

Both inputs must be above zero. At exactly 60 bpm RR equals 1 s, so QTc equals the measured QT. Bazett's formula tends to over-correct at fast heart rates and under-correct at slow ones, which is why other formulas exist; this tool only uses Bazett. It is a calculation aid and does not interpret the number or replace a clinician's reading of the ECG.

Common mistakes

• Entering QT in seconds (0.38). The field expects milliseconds, so the result would be meaningless.
• Using the RR interval in the heart rate box. The field wants beats per minute.
• Applying Bazett at very fast or slow heart rates and trusting it fully; it distorts the value at those extremes.
• Reading the QT from a single beat when the rhythm is irregular, as in atrial fibrillation, where an average over several beats is normally used.
• Comparing the corrected figure with limits that were set for a different formula.