QTc Calculator
Correct the QT interval for heart rate (Bazett’s formula) and flag prolongation and torsades risk.
Enter the measured QT interval and heart rate to calculate.
Why correct the QT
The raw QT interval shortens as the heart rate rises and lengthens as it falls, so a raw QT can’t be compared across rates. Bazett’s formula (QTc = QT ÷ √RR) normalizes it to a rate of 60 — the most widely used correction, though it over-corrects at fast rates and under-corrects at slow rates.
A QTc > 500 ms markedly raises the risk of torsades de pointes. Common culprits: antiarrhythmics, many antiemetics and antipsychotics, methadone, some antibiotics (e.g. macrolides, fluoroquinolones), and low potassium or magnesium.
Educational use only. QTc thresholds vary by source and the QT is best measured on a 12-lead ECG; medication and monitoring decisions follow provider orders and your facility’s protocols. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.