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QTc Calculator

Health

Calculate the corrected QT interval using the Bazett, Fridericia, Framingham, and Hodges formulas side by side, with normal-range interpretation by sex.

Measured QT Interval
ms
Heart Rate
bpm
Sex

All Four Correction Formulas

Bazett0 ms
Fridericia0 ms
Framingham0 ms
Hodges0 ms

Bazett is shown as the primary result because it remains the most widely used formula in clinical practice, though it over-corrects at fast heart rates. Fridericia and Hodges are often more accurate outside a normal resting heart rate range.

QTc (Bazett)

0ms

Normal: <440 ms

—

Not a substitute for clinical evaluation. A prolonged QTc should be reviewed by a qualified healthcare provider alongside medication history and electrolyte status.

What is a QTc?

The QTc Calculator computes the heart-rate-corrected QT interval using four published formulas — Bazett, Fridericia, Framingham, and Hodges — shown side by side so you can compare how each one handles the same measured QT interval and heart rate.

Enter your measured QT interval, heart rate, and sex to see all four corrected values along with a normal-range interpretation based on the Bazett result, the formula most widely used in day-to-day clinical practice. For related ECG measurement tools, see the ECG Heart Rate Calculator and ECG Boxes-to-Seconds Calculator.

How to use this QTc calculator

  1. Enter the Measured QT Interval in milliseconds, as read from the ECG.
  2. Enter the Heart Rate in beats per minute.
  3. Select Male or Female to apply the correct normal-range threshold.
  4. Review the Bazett QTc result and its interpretation in the result card.
  5. Compare the Fridericia, Framingham, and Hodges values shown alongside Bazett.
  6. Discuss any prolonged or borderline result with a qualified healthcare provider before making any medication decision.

Formula & Methodology

RR interval (seconds) = 60 ÷ heart rate (bpm).

- Bazett: QTc = QT ÷ √RR
- Fridericia: QTc = QT ÷ ∛RR
- Framingham: QTc = QT + 154 × (1 − RR)
- Hodges: QTc = QT + 1.75 × (heart rate − 60)

Normal QTc (Bazett): under 440 ms for men, under 460 ms for women. QTc above 500 ms carries a materially higher risk of torsades de pointes.

Worked example: A measured QT interval of 400 ms at a heart rate of 90 bpm gives an RR interval of 60 ÷ 90 ≈ 0.667 s. Bazett QTc = 400 ÷ √0.667 ≈ 490 ms; Fridericia QTc = 400 ÷ ∛0.667 ≈ 458 ms — illustrating how Bazett over-corrects at a faster-than-resting heart rate compared to Fridericia.

Frequently Asked Questions

QTc is the QT interval on an ECG corrected for heart rate, because the raw QT interval naturally shortens as heart rate increases and lengthens as it decreases. Correcting for heart rate allows a meaningful comparison of ventricular repolarization time regardless of the current heart rate.
Bazett's formula remains the most widely used in clinical practice and is shown as the primary result here, but it is known to over-correct at fast heart rates and under-correct at slow ones. Fridericia's formula is often considered more accurate outside a normal resting heart rate range, which is why this calculator shows all four formulas side by side.
A QTc under 440 ms is generally considered normal for men, and under 460 ms for women. Values above 500 ms are associated with a materially higher risk of torsades de pointes, a dangerous ventricular arrhythmia.
Each formula uses a different mathematical relationship to the RR interval: Bazett divides by the square root, Fridericia divides by the cube root, and Framingham and Hodges use linear adjustments instead of division. These different approaches produce increasingly divergent results the further the heart rate is from a normal resting rate.
Prolonged QTc can result from congenital long QT syndrome, numerous medications (including some antiarrhythmics, antibiotics, and antipsychotics), electrolyte abnormalities like low potassium or magnesium, and other cardiac or systemic conditions. Identifying the specific cause requires evaluation by a qualified healthcare provider.
Yes — short QT syndrome is a separate, rarer condition associated with an increased risk of arrhythmia, though this calculator focuses on the more commonly encountered prolonged QTc thresholds. Any unusually short QTc should also be reviewed by a physician.
No — this calculator performs the standard rate-correction formulas on the measured QT interval as entered, and does not adjust for a widened QRS from bundle branch block, which some specialized correction methods do account for separately.
RR interval in seconds equals 60 divided by the heart rate in beats per minute. This calculator computes RR automatically from the heart rate you enter and uses it in each of the four correction formulas.
Women generally have slightly longer baseline QTc intervals than men across the population, so clinical thresholds for a 'prolonged' QTc are set a bit higher for women (460 ms) than for men (440 ms) to reflect this physiologic difference.
No — never stop or adjust a medication based on this calculator alone. Decisions about QT-prolonging medications must be made by the prescribing physician, who will weigh the calculated QTc alongside your full medication list, electrolytes, and clinical context.
No — this calculator is for informational and educational purposes only and performs the standard rate-correction arithmetic on values you provide. A full ECG interpretation, including QTc, should always be reviewed by a qualified healthcare provider.
The ECG Heart Rate Calculator and ECG Boxes-to-Seconds Calculator help derive the heart rate and interval measurements from an ECG strip, which can then be entered here to calculate QTc using any of the four formulas.
Also known as
corrected QT interval calculatorBazett formula calculatorFridericia QTc calculatorQT correction calculatorlong QT syndrome calculator