QTc Calculator

QT interval correction using Bazett, Fridericia, Sagie/Framingham, Hodges, Rautaharju, Mayeda, Kawataki, and Goto.

Results

QTc Bazett 414
QTc Fridericia 414
QTlc Sagie/Framingham 414
QTc Hodges 414
Additional Formulas
QTc Rautaharju a 414
Rautaharju b, male 414
Rautaharju b, female 414
QTc Mayeda 414
QTc Kawataki 414
QTc Goto 414

Position between the ESC Guidelines 2022 thresholds

QTc Fridericia compared with the general population according to Vandenberk et al., 2016

QTc values are rounded to milliseconds. Yellow and red mark threshold crossings according to the ESC Guidelines 2022.

Which Formula Should I Use?

QTc is most reliable when the ECG is recorded near a heart rate of 60 beats per minute. Depending on the setting and on borderline results, repeating the ECG may be worthwhile.

This page cannot make a definitive choice for you. I personally would use Fridericia's formula.

  1. Vandenberk et al., 2016 compared several correction formulas in more than 6,600 adult, mostly European subjects. Fridericia and Sagie/Framingham performed better than Bazett.
  2. Bazett often overestimates QTc at higher heart rates. This can lead to false long-QT diagnoses and unnecessary treatment changes.
  3. The Framingham formula is based on a very large sample size and is often close to Fridericia at heart rates between 60 and 100.
  4. In research settings, formulas that take age and sex into account, such as Rautaharju, may be useful.
  5. Bazett is the most widely used formula for historical reasons and is used by many ECG machines.

Measurement Methods

The common methods for measuring the QT interval on an ECG are the threshold and tangent methods. The tangent method generally provides more accurate results. Automated systems sometimes tend to estimate QTc too high.

Thresholds for Long-/Short-QT Syndrome

Thresholds remain controversial. According to the ESC Guidelines 2022:

  • Long-QT syndrome: from 480 ms, even if asymptomatic; from 460 ms if symptomatic.
  • Short-QT syndrome: up to 320 ms, even if asymptomatic; up to 360 ms with symptoms or additional factors.

QTc Distribution in the Population

The chart in the calculator is based on Vandenberk et al., 2016 and assumes a normal distribution for QTc by Fridericia with a mean of 414 ms and a standard deviation of 25 ms.

Formulas

QTc Bazett QTc = QT / sqrt(RR)
QTc Fridericia QTc = QT / RR^(1/3)
QTlc Sagie / Framingham QTlc = 1000 * (QT / 1000 + 0.154 * (1 - RR))
QTc Hodges QTc = QT + 1.75 * (HR - 60)
QTc Rautaharju a QTc = QT * (120 + HR) / 180
QTc Rautaharju b Men: QTc = QT + 387 * (1 - RR^0.37) Women: QTc = QT + 409 * (1 - RR^0.39)
QTc Mayeda QTc = QT / RR^0.604
QTc Kawataki QTc = QT / RR^0.25
QTc Goto QTc = QT / RR^0.3409
Heart rate and RR interval RR = 60 / HR

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