Which QTc formula should I use?

Bazett is the most widely cited and used in clinical practice, but it over-corrects at high heart rates. Fridericia is preferred when HR is above 80 bpm. Framingham and Hodges provide linear corrections and may be more accurate across a wider HR range. When in doubt, consider all four results together.

What is a normal QTc value?

Normal QTc is generally below 440 ms in men and below 460 ms in women. Values of 440–470 ms (men) or 460–480 ms (women) are considered borderline. Values above 500 ms are associated with significantly increased risk of Torsades de Pointes.

How do I measure the QT interval from an ECG?

Measure from the beginning of the QRS complex to the end of the T wave in leads II, V5, or V6. Use the longest QT interval seen across all leads. Avoid measuring in leads with U waves merged into the T wave.

Why does my QTc differ between formulas?

Each formula uses a different mathematical relationship between QT and RR interval. Bazett uses a square-root correction, Fridericia uses a cube-root, while Framingham and Hodges use linear models. Differences are most pronounced when heart rate is significantly above or below 60 bpm.

Is this tool a substitute for clinical judgment?

No. This calculator is for informational and educational purposes only. Clinical decisions about QT prolongation must be made by qualified healthcare professionals who consider the full clinical picture, patient history, and concurrent medications.

What QT interval range can I enter?

Clinically meaningful QT intervals range from about 250 ms to 650 ms. Heart rate should be between 30 and 200 bpm for reliable correction. Outside these ranges, correction formulas become less reliable.

QTc Calculator

Enter QT interval and heart rate to calculate corrected QTc using four standard formulas with normal range interpretation.

ECG Measurements

QT Interval (ms)

Typical range: 250 – 650 ms

Heart Rate (bpm)

Normal resting: 60 – 100 bpm

Sex (for thresholds)

Male Female

Enter QT interval and heart rate, then click Calculate QTc.

Summary

The QTc Calculator computes the heart-rate-corrected QT interval (QTc) from a raw QT measurement and current heart rate. Prolonged QTc increases the risk of life-threatening arrhythmias such as Torsades de Pointes. Four widely accepted correction formulas are supported: Bazett (most common), Fridericia (preferred at faster rates), Framingham (linear correction), and Hodges (linear correction with independent validation).

How it works

Enter the measured QT interval in milliseconds (read from ECG).
Enter the heart rate in beats per minute (bpm).
The tool calculates the RR interval from the heart rate.
Each of the four formulas applies its correction to produce QTc.
Results are color-coded: normal, borderline, or prolonged per clinical thresholds.
All calculations run instantly in your browser — no data is sent to any server.

Use cases

Screen patients for drug-induced QT prolongation before prescribing.
Monitor QTc during treatment with antiarrhythmics, antipsychotics, or antibiotics.
Compare multiple correction methods when heart rate is outside the 60–100 bpm range.
Quickly assess ECG strips in emergency or cardiology settings.
Educational use for medical students learning ECG interpretation.
Telemedicine triage when a remote patient shares ECG measurements.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu