Correct the QT interval for heart rate with the Bazett, Fridericia, Framingham and Hodges formulas and compare it with male and female limits.
ms
bpm
Enter the values to see the result here.
Calculation aids only. They do not replace clinical judgement or the drug reference. Verify every dose before using it on a patient.
Formula
With QT in milliseconds, heart rate HR in beats per minute and RR=60/HR in seconds:
Bazett: RRQTFridericia: 3RRQT
Framingham is QT+154(1−RR) and Hodges is QT+1.75(HR−60). Upper limits of normal are about 450 ms for men and 460 ms for women; 500 ms or more is high risk.
Worked example
A patient has a QT of 400 ms at 75 beats per minute.
RR=60/75=0.8 s.
Bazett: 400/0.8=447 ms, borderline for a man.
Fridericia: 400/30.8=431 ms, normal.
The two formulas disagree by 16 ms at this rate, which is why the formula you use must be stated.
Common mistakes
Entering the QT in seconds. This tool expects milliseconds.
Comparing a Bazett value from one source with a Fridericia value from another.
Using the heart rate printed by the machine over a different time window than the QT measurement.
Acting on one number. Trends over time and the clinical picture matter more.
Frequently asked questions
Which QTc formula is best?
Bazett is the one most often printed on ECG machines, but it overcorrects when the heart rate is above about 100 and undercorrects below 60. Fridericia and Framingham behave better across a wider range, and many drug-safety studies now use Fridericia.
What QTc is dangerous?
A QTc of 500 ms or more, or an increase of 60 ms or more from baseline, is associated with a higher risk of torsades de pointes. Many drugs, low potassium, low magnesium and some inherited conditions prolong the QT.
How should I measure the QT interval?
From the start of the QRS complex to the end of the T wave, preferably in lead II or V5, averaged over several beats. When a U wave or atrial fibrillation is present measurement is harder and specialist review is wise.