QTc Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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Cardiovascular numbers become useful only when the equation behind them is clear. QTc Calculator turns the specific measurements in this tool into a focused hemodynamic or risk estimate.

What this calculator does

QTc Calculator uses QT interval, Heart rate, and RR interval to calculate corrected QT interval. It is built around the exact fields displayed in this plugin rather than a generic version of the topic. Where supported, it also shows RR interval, Fridericia, and Framingham so the primary result is easier to place in context. Cardiovascular formulas are sensitive to measurement technique and clinical context. A mathematically correct output can still be misleading if the input was obtained under a different physiologic condition, with a different assay, or outside the population for which the score was developed.

How to use it

Enter or select QT interval, Heart rate, and RR interval. Use the units offered by the calculator and choose the option that matches the actual clinical or timing situation. Check date entries and laboratory units before relying on the output. When the formula combines measurements, use values obtained under the same assessment or physiologic conditions whenever possible.

How the calculation works

The calculator first establishes the R–R interval from the direct R–R entry or from heart rate. It then reports Bazett QTc as the primary value and also calculates Fridericia, Framingham, and Hodges corrections: QT/√RR, QT/∛RR, QT + 0.154(1−RR), and QT + 0.00175(HR−60), respectively. QT is converted from milliseconds to seconds where required and returned in milliseconds.

Example

Using the sample values prefilled in this calculator, the primary result is 415.7 ms (QTc (Bazett)), RR interval is 0.75 s, and Fridericia is 396.2 ms. This worked example shows how the plugin’s own default inputs flow through the implemented method; replace them with the correct patient, laboratory, imaging, or personal values before interpreting a result.

How to interpret the result

Read the output as qtc (bazett) generated by this specific formula or score. The number is most useful when compared with the clinical context and, when appropriate, serial measurements or the current guideline pathway for the condition. A boundary value should not be overinterpreted as a sudden change in physiology.

Limitations and notes

QT correction formulas disagree, especially at very slow or fast heart rates. Bazett often overcorrects at higher rates and undercorrects at lower rates, which is why this calculator also displays other formulas. Manual QT measurement, QRS duration, rhythm, medications, electrolytes, and congenital risk all matter clinically.