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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.

Reviewed by the thecalcu.com team · Last updated July 21, 2026

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

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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.

Why Use a QTc Calculator?

Each correction formula uses a different mathematical relationship to the RR interval, square root, cube root, or linear adjustment, and manually working through even one of them is tedious, let alone all four. This calculator computes all four instantly and highlights which formula is used for the headline risk interpretation.

It's especially useful for comparing how the choice of formula affects the corrected value at heart rates far from a normal resting rate, where the formulas diverge the most.

Who Should Use This Calculator?

Nursing and medical students learning ECG interpretation can use this tool to check worked QTc examples across all four common formulas. Clinicians reviewing a QT interval at an unusual heart rate may use it to quickly compare how Bazett's result differs from Fridericia's or Hodges's.

This calculator is strictly for informational and educational purposes and is not a substitute for a qualified healthcare provider's interpretation of an ECG or any decision about starting, continuing, or stopping a medication.

What Insights Does the QTc Calculator Give You?

Bazett QTc is the primary, highlighted result, reflecting the most widely used correction formula in routine clinical practice.

Fridericia, Framingham, and Hodges QTc are shown alongside Bazett for comparison, since each formula handles heart rates away from a normal resting range differently.

Interpretation classifies the Bazett result as normal, prolonged, or high risk, using sex-specific thresholds (440 ms for men, 460 ms for women, and 500 ms as the high-risk cutoff for both).

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.
Show formula & methodology ↓Show less ↑

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

What is QTc and why is it corrected for heart rate?
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.
Which QTc formula should I use?
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.
What is a normal QTc value?
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.
Why do the four formulas give different results?
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.
What causes a prolonged QTc?
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.
Can a short QTc also be dangerous?
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.
Does this calculator account for QRS duration or bundle branch block?
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.
How is the RR interval calculated?
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.
Why does sex affect the normal QTc threshold?
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.
Should I stop a medication if my QTc looks prolonged?
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.
Is this calculator a substitute for a cardiologist's ECG interpretation?
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.
How does QTc relate to heart rate calculators like ECG heart rate tools?
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