QTc Calculator (Corrected QT Interval)
Enter the QT interval and heart rate to get the corrected QT with four formulas.
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QTc Calculator (Corrected QT Interval) by TheCalcTools
How the QTc Calculator (Corrected QT Interval) works
The QT interval shortens as heart rate rises, so it is corrected to a rate of 60 bpm (RR = 1 second). Bazett divides by the square root of RR; it over-corrects at fast rates, where Fridericia (cube root) or Framingham are often preferred.
Common thresholds for a prolonged QTc are above 450 ms in men and above 470 ms in women; above 500 ms is associated with a higher risk of arrhythmia. Interpretation belongs to a clinician.
The formula
Worked example
Using the default values shown in the calculator:
| QT interval (ms) | 400 |
|---|---|
| Rate given as | Heart rate (bpm) |
| Heart rate (bpm) | 75 |
| RR interval (ms) | 800 |
- At 75 bpm, RR = 0.8 s. Bazett: 400 ÷ √0.8 = 447 ms; Fridericia 431 ms.
Result:
| Bazett (ms) | 447 |
|---|---|
| Fridericia (ms) | 431 |
| Framingham (ms) | 431 |
| Hodges (ms) | 426 |
| Bazett QTc compared with common limits | Within common limits |
Frequently asked questions
Which formula should I use?
Bazett is the most widely used but least accurate away from 60 bpm. Many cardiologists prefer Fridericia, especially for drug safety monitoring.
Sources and further reading
- Wikipedia: QT interval
- Vandenberk B et al. (2016) Which QT correction formulae to use for QT monitoring? J Am Heart Assoc 5:e003264
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This calculator gives general estimates for information and education. It is not medical advice and does not diagnose anything. Talk to a qualified health professional about your own situation. See our disclaimer.