QTc calculator
Rate-corrected QT interval by Bazett, Fridericia, Framingham and Hodges.
Prolongation thresholds differ between men and women.
This tool runs entirely in your browser. Nothing you enter is sent to VitalFax or stored anywhere.
Enter the values above
This is a reference implementation of a published formula, provided for use by qualified healthcare professionals. It does not diagnose, does not account for the individual circumstances of any patient, and is not a recommendation for treatment. Confirm every result against your own institutional guidance before acting on it. Clinical judgement always takes precedence over a calculator.
About this calculation
The QT interval shortens as heart rate rises, so it is corrected to a notional rate of 60 beats per minute before being compared against a threshold. Four corrections are in common use and they disagree substantially away from 60 bpm, which is why all four are shown.
Formula
Bazett: QT ÷ √RR · Fridericia: QT ÷ ∛RR · Framingham: QT + 154 × (1 − RR) · Hodges: QT + 1.75 × (HR − 60)
- Source
- Bazett (1920), Fridericia (1920), Sagie et al. Framingham (1992), Hodges (1983)
- Methodology version
- 1.0.0
- Last reviewed
- 2026-10-28
What this does not account for
- Bazett is the most widely quoted and the least accurate away from 60 bpm: it overcorrects at tachycardia and undercorrects at bradycardia. Fridericia is generally preferred at the extremes.
- No correction is valid in atrial fibrillation, where RR varies beat to beat. Average several beats and treat the result as indicative only.
- In bundle branch block or a paced rhythm the QT includes a widened QRS, so the raw interval overstates repolarisation time.
- Thresholds are approximate and differ by sex. A single value does not establish risk on its own.