QTc Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026
Disclaimer: This calculator is provided for informational and educational purposes only and does not constitute financial, medical, legal, or other professional advice. Always consult a qualified professional before making decisions based on these results.
Correcting QT interval for heart rate
The QT interval on an ECG naturally shortens at faster heart rates and lengthens at slower ones - Bazett's formula, published in 1920, corrects for this so QT intervals can be meaningfully compared across different heart rates.
Worked example
For a QT interval of 400ms with an 800ms RR interval:
QTc = 400 / sqrt(0.8) = 447.2 ms (Within commonly cited normal range)
Bazett's formula is known to over-correct at heart rates far from 60 bpm (very fast or very slow rates), which is why alternative formulas like Fridericia's or the Framingham formula are sometimes preferred at extreme heart rates for more accurate correction.
This is an informational tool only - QTc interpretation always requires review by a qualified healthcare provider, since a prolonged QTc carries risk of dangerous arrhythmias and may be influenced by medications, electrolyte abnormalities, and underlying cardiac conditions.