Correct the QT interval for heart rate by both the Bazett and Fridericia formulas, with sex-based prolongation flags.
Result
How to use this tool
Enter the QT interval in ms.
Enter the heart rate.
Read both corrected values.
Discuss any prolonged value promptly, with a medicines and electrolyte review.
Formula & worked example
QT 400 ms at 75 beats/min gives a Bazett QTc of 447 ms and a Fridericia QTc of 431 ms.
Limitations — read this before you rely on it
Calculation aid only. Manual QT measurement varies, Bazett distorts at rate extremes, and thresholds are approximate guides. This tool is for education only and is not medical advice. Talk to a clinician about any result that worries you, and never change treatment because of a calculator result.
Frequently asked questions
The QT interval corrected for heart rate, so readings at different rates can be compared.
Bazett is the classic formula but distorts at fast or slow rates; Fridericia is more stable outside 60-100 beats/min.
Roughly above 450 ms in men and 470 ms in women, with higher values carrying higher arrhythmia risk.
Many medicines, low potassium, magnesium or calcium, and inherited long-QT syndromes.
Risk rises with length, but symptoms, electrolytes and medicines decide urgency — seek prompt review.