QTc Calculator
Calculate the Corrected QT (QTc) interval from an ECG to identify patients at risk of dangerous arrhythmias. Compare Bazett, Fridericia, Framingham, and Hodges formulas instantly.
Last updated: March 3, 2026
High Heart Rate Warning
If the patient's heart rate is greater than 100 bpm, remember that Bazett's formula tends to artificially over-correct the QT, creating false positives. In these cases, Fridericia or Framingham is preferred by many cardiologists.
400
msAlternative Formulas
Comparing The QTc Formulas
Because the raw QT interval changes with heart rate, mathematicians have developed several methods to "correct" it. Here is how they differ.
Bazett's Formula
The oldest and most common formula baked into most ECG machines. It uses a square root transformation. However, it is flawed: it over-corrects at fast heart rates (making normal QT intervals look prolonged) and under-corrects at slow heart rates.
Fridericia's Formula
Uses a cube root instead of a square root. This formula provides a much more robust and accurate correction at temperature extremes, specifically at faster heart rates (> 100 bpm) and is strongly favored in many modern clinical trials.
Framingham Formula
Derived from the massive Framingham Heart Study, this is a linear regression formula (`QT + 154 * (1 - RR)`). It is highly accurate and provides a more consistent risk prediction across all heart rates than Bazett.
Hodges Formula
Another linear equation (`QT + 1.75 * (HR - 60)`). Like Framingham and Fridericia, it tends to outperform Bazett at non-standard heart rates, avoiding the artificial over-correction seen during tachycardia.
Frequently Asked Questions
Share With Medical Colleagues
A fast, reliable tool for interpreting ECGs on the wards.