QTc calculator (Bazett, Fridericia)
Enter the measured QT interval and heart rate to get QTc by four formulas, compared with accepted prolongation limits.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter qt interval, heart rate and sex.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
RR = 60 ÷ heart rate (s). Bazett: QT ÷ √RR. Fridericia: QT ÷ ∛RR. Framingham: QT + 154 × (1 - RR). Hodges: QT + 1.75 × (HR - 60). The flag uses Bazett: prolonged from 450 in men and 460 in women, markedly prolonged from 500.
Example
Inputs: QT interval = 400 ms, Heart rate = 75 bpm, Sex = Male. Result: QTc (Bazett): 447 ms; QTc (Fridericia): 431 ms; QTc (Framingham): 431 ms.
Limits and caveats
- Bazett overcorrects at fast heart rates and undercorrects at slow ones, so several formulas are shown.
- Manual QT measurement varies between readers, and the result is only as good as your measurement.
- An educational estimate that does not replace assessment by a doctor or pharmacist.
Questions about this tool
Which formula should I use?
Bazett is the most used but overcorrects at fast rates, so many prefer Fridericia or Framingham when the rate is far from 60.
When is QTc prolonged?
Per the 2009 AHA/ACCF/HRS recommendations: 450 ms or more in men and 460 ms or more in women, with 500 ms or more markedly prolonged.
Why does QTc equal QT at a rate of 60?
At 60 beats per minute the RR interval is exactly 1 second, and every formula is set to return QT unchanged there.