QTc Calculator

QTc Calculator for Cardiology. Marked QTc prolongation warrants assessment of medications, electrolytes, measurement quality and clinical context. A threshold is a warning marker, not a probability of torsades or a diagnosis of congenital long-QT syndrome.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

The tool accepts QT in milliseconds and heart rate, derives RR as 60/heart rate in seconds, and offers Bazett, Fridericia, Framingham and Hodges corrections.

When to use this calculator

To support interpretation of a carefully measured QT interval. Record the correction formula when comparing serial ECGs.

Inputs used

  • Measured QT interval in milliseconds
  • Heart rate in beats/min
  • Correction formula
  • Sex category used for displayed thresholds

Clinical interpretation

Marked QTc prolongation warrants assessment of medications, electrolytes, measurement quality and clinical context. A threshold is a warning marker, not a probability of torsades or a diagnosis of congenital long-QT syndrome.

Worked example

QT 440 ms at 100 beats/min gives RR 0.6 seconds: Bazett 568.0 ms, Fridericia 521.7 ms, Framingham 501.6 ms and Hodges 510.0 ms. All four exceed 500 ms; the lower alternatives do not remove concern.

Limitations and safety notes

Heart-rate extremes, irregular rhythms and a wide QRS complicate interpretation. The derived RR is an average estimate and does not replace beat selection and manual ECG review.

Frequently asked questions

Can I compare different formulas as though they are interchangeable?

No. They have different rate behavior; consistent serial methods improve interpretability.

Does the tool accept RR directly?

No. This implementation derives RR from heart rate.

References

  • Drew BJ et al. Prevention of Torsade de Pointes in Hospital Settings. AHA/ACCF Scientific Statement. 2010. https://www.jacc.org/doi/10.1016/j.jacc.2010.01.001
  • A comparison of commonly used QT correction formulae: The effect of heart rate on the QTc of normal ECGs. Journal of Electrocardiology. 2004. https://www.sciencedirect.com/science/article/abs/pii/S0022073604001001

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 7, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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