QTc Calculator (Bazett)

About this calculator

The QT interval on an ECG — the time from ventricular depolarization to repolarization — naturally shortens as heart rate increases, so clinicians correct it for heart rate to get the QTc (corrected QT). Bazett's formula, the most widely used correction, is QTc = QT / √RR, where RR is the interval between heartbeats in seconds (60/heart rate).

A prolonged QTc (generally above 450ms in men or 460ms in women) is a risk marker for torsades de pointes, a dangerous ventricular arrhythmia, and is monitored closely when prescribing QT-prolonging medications like certain antibiotics, antipsychotics, and antiarrhythmics.

Cardiologists and emergency physicians reading ECGs, pharmacists screening for drug interactions that prolong QT, and nursing and medical students learning ECG interpretation all use Bazett's formula, though clinicians note it over-corrects at high heart rates compared to alternatives like Fridericia's formula.