Corrected QT Interval (QTc) Calculator

Calculate corrected QT interval (QTc) using Bazett, Fridericia, Framingham, and Hodges formulas.

For educational and clinical reference. Not a substitute for medical judgment. See the medical disclaimer.
QTc — Bazett
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QTc — Fridericia
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QTc — Framingham
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QTc — Hodges
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Classification (Bazett)
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References

  1. Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370.
  2. Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469-486.
  3. Sagie A, Larson MG, Goldberg RJ, et al. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol. 1992;70(7):797-801.
  4. Hodges M, Salerno D, Erlien D. Bazett's QT correction reviewed. J Am Coll Cardiol. 1983;1:694.

How to use

  1. Enter measured QT interval (ms) and heart rate (bpm).
  2. All four QTc formulas update instantly.
  3. Classification follows AHA/HRS criteria.

Frequently asked questions

Which QTc formula should I use?

Bazett is the historic standard but over-corrects at high heart rates and under-corrects at low rates. Fridericia and Framingham perform better across HR; Hodges is simple and HR-linear.

What are the QTc thresholds?

Men: normal ≤ 449 ms; borderline 450–469; prolonged ≥ 470. Women: normal ≤ 459; borderline 460–479; prolonged ≥ 480. QTc < 360 ms is considered short.

Why is QTc clinically important?

Prolonged QTc increases the risk of torsades de pointes and sudden cardiac death — especially with drugs that further prolong QT (antiarrhythmics, antibiotics, antipsychotics, etc.).

How is QT measured?

QT is measured from the start of the Q wave to the end of the T wave on a 12-lead ECG. Use leads II, V5, or V6 by convention.

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