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Corrected QT (QTc) Calculator (Bazett/Fridericia/Framingham)

· Last updated：2026-08-09

This tool is for informational purposes only and does not constitute medical, financial, or legal advice; consult a qualified professional for advice.

Calculate the heart-rate–corrected QT interval (QTc) with three formulae. Bazett (1920): QTc = QT/√RR (classic; over-corrects at high HR, under-corrects at low HR). Fridericia (1920): QTc = QT/RR^(1/3) — more accurate across a wide HR range, preferred for drug/QT studies. Framingham (1992): QTc = QT + 0.154×(1 − RR) — simple linear regression. RR is derived from heart rate (RR = 60/HR) when not provided; QT and QTc in ms. Thresholds: men > 450 ms borderline / > 480 ms prolonged; women > 460 ms borderline / > 480 ms prolonged; > 500 ms markedly prolonged. Derived from Bazett 1920, Fridericia 1920, Sagie/Framingham 1992, AHA 2009, ICH E14, and MDCalc. Not medical advice.

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Tool usage guide

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Key facts

Category
Health
Input types
select, number
Output type
json
Sample coverage
4
API ready
Yes

Overview

Calculate the heart-rate-corrected QT interval (QTc) in milliseconds using the Bazett, Fridericia, or Framingham formula. Enter a measured QT interval and heart rate, or provide an RR interval directly; the result includes the QTc value, RR interval, selected method, and category. This calculator is not medical advice.

When to use

  • Estimate QTc from an ECG-measured QT interval and heart rate.
  • Compare Bazett, Fridericia, and Framingham correction methods.
  • Review QTc values against sex-specific reference thresholds during ECG or medication assessment.

How it works

  1. 1Select the correction formula and sex, then enter the QT interval in milliseconds.
  2. 2Enter heart rate in bpm to derive RR as 60 divided by heart rate, or provide an RR interval in seconds.
  3. 3If both are provided, the supplied RR interval overrides the heart-rate-derived value.
  4. 4The calculator returns QTc in milliseconds, the selected formula, RR interval, and a QTc category.

Use cases

  • ECG review using a measured QT interval and heart rate.
  • Cardiology and clinical research comparisons of QTc correction formulas.
  • Medication or risk assessment where QT prolongation requires further clinical review.

Examples

1. Bazett QTc at a resting heart rate

Clinician reviewing an ECG

Background

An ECG shows a QT interval of 380 ms and a heart rate of 75 bpm in a male patient.

Problem

Calculate the QTc and determine whether it falls within the stated male reference limit.

How to use

Select Bazett and Male, enter QT as 380 ms and heart rate as 75 bpm, then calculate.

Formula: Bazett; Sex: Male; QT: 380 ms; Heart rate: 75 bpm; Decimal places: 1

Outcome

RR is 0.8 s and QTc is approximately 424.9 ms, categorized as QTc normal.

2. Fridericia QTc at a low heart rate

Researcher comparing correction methods

Background

A female patient has a measured QT interval of 440 ms and a heart rate of 50 bpm.

Problem

Calculate QTc with Fridericia, a method used across a wide heart-rate range.

How to use

Select Fridericia and Female, enter QT as 440 ms and heart rate as 50 bpm, then calculate.

FAQ

What inputs are required?

You must select a formula and sex and enter the measured QT interval in milliseconds. Heart rate or RR interval is also needed to calculate QTc.

Can I enter an RR interval instead of heart rate?

Yes. Enter RR in seconds. When provided, it overrides the RR derived from heart rate.

Which QTc formulas are available?

The calculator supports Bazett, Fridericia, and Framingham correction formulas.

What do the QTc categories mean?

For men, values above 450 ms are borderline and above 480 ms are prolonged. For women, values above 460 ms are borderline and above 480 ms are prolonged; values above 500 ms are markedly prolonged.

Is this calculator medical advice?

No. Use the result as a calculation aid and discuss ECG findings, medications, and clinical decisions with a qualified healthcare professional.

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Formula: Fridericia; Sex: Female; QT: 440 ms; Heart rate: 50 bpm; Decimal places: 1

Outcome

RR is 1.2 s and QTc is approximately 414.1 ms, categorized as QTc normal.