Corrected QT Interval Calculator

Calculate corrected QT interval using Bazett, Fridericia, or Framingham formula.

QT interval (ms) (ms)

Measured from ECG

Heart rate (bpm) (bpm)

Formula

Please check your inputs and try again.

Worked Examples

Example 1: QT=420ms at HR=60

RR=1000ms, Bazett: QTc=420/√1.0

Result: 420 ms — normal

At 60 bpm, QTc = QT for Bazett

Example 2: QT=420ms at HR=100

RR=600ms, Bazett: QTc=420/√0.6

Result: 542 ms — CRITICAL

Tachycardia unmasks QT prolongation

Frequently Asked Questions

Which drugs prolong QT?

Antibiotics (azithromycin, fluoroquinolones), antipsychotics (haloperidol, quetiapine), antiarrhythmics (amiodarone, sotalol), antiemetics (ondansetron), antifungals (fluconazole). Always check crediblemeds.org.

When is QTc prolongation dangerous?

QTc >500 ms carries significant risk of Torsades de Pointes (TdP), a potentially fatal ventricular arrhythmia. Risk increases with hypokalemia, hypomagnesemia, bradycardia, and female sex.