QTc Calculator (Bazett, Fridericia)

Correct the QT interval for heart rate with the Bazett, Fridericia, Framingham and Hodges formulas. Example: a QT of 400 ms at 75 bpm gives a QTc of 447 ms (Bazett) or 431 ms (Fridericia).

How to use the QTc Calculator (Bazett, Fridericia)

1. Enter the values in the fields.
2. Press Calculate to see the result with the steps shown.

Formula and method

Bazett QTc = QT / sqrt(RR). Fridericia QTc = QT / RR^(1/3). Framingham = QT + 154 x (1 – RR). Hodges = QT + 1.75 x (HR – 60). RR = 60 / heart rate in seconds.

QTc reference values

QTc at different heart rates for QT 400 ms

Which formula to use

Bazett is the most common but biased at high or low rates. Fridericia and Framingham are more stable, and many drug-safety trials now use Fridericia.

Medications and electrolytes

Several antibiotics, antipsychotics, antiemetics and antiarrhythmics prolong QT, and low potassium, magnesium or calcium add risk. This calculator is for education and is not medical advice. Decisions about diagnosis and treatment belong with a qualified clinician.

Frequently asked questions

What is a normal QTc?

Below about 450 ms for men and 460 ms for women.

What is a dangerous QTc?

500 ms or more, or an increase of over 60 ms from baseline.

Which formula is best?

Fridericia is preferred at faster heart rates.

Why correct QT?

QT shortens as heart rate rises.

Can I measure QT myself?

Use a clinician-read ECG.

Does a long QT need treatment?

That depends on cause and symptoms; see a clinician.

Sources

• American Heart Association: Long QT syndrome
• NHLBI: Long QT syndrome

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