Calcoid

QTc Calculator

Correct the QT interval for heart rate using Bazett, Fridericia, Framingham, or Hodges. Flags sex-specific prolongation thresholds.

ECG values

Raw QT interval from the ECG, in milliseconds. Typical adult range is 350 to 440 ms.

Used only to set the prolongation threshold (450 ms for males, 460 ms for females).

RR (ms) is computed as 60000 / bpm.

Bazett is the default because it is the most widely reported, but Fridericia and Framingham are more reliable outside 60 to 100 bpm.

Corrected QT (Bazett)

400 ms

Normal QTc range

QTc is in the normal range. Routine monitoring still applies if the patient is taking QT-prolonging medications or has structural heart disease. Bazett tends to overcorrect at fast heart rates, so cross-check the Fridericia value as well.

Heart rate
60 bpm
RR interval
1,000 ms

Comparison across formulas

Bazett
400 ms
Fridericia
400 ms
Framingham
400 ms
Hodges
400 ms

Medical disclaimer

This calculator is for educational use only. It is not a diagnosis and not a substitute for clinical judgment. QT measurement is operator dependent, electrolyte abnormalities and QT-prolonging medications can shift QTc substantially, and no single formula is universally accurate across all heart rates. If a real patient has a prolonged QTc, symptoms of arrhythmia, or is starting a QT-prolonging drug, consult a clinician or cardiologist before acting on this estimate.

QTc Formula Comparison

All formulas correct a measured QT interval for heart rate. The example uses QT 400 ms at 100 bpm.

FormulaInputsQTc resultCalculator use
BazettQT 400 ms, HR 100516.4 msQT / sqrt(RR)
FridericiaQT 400 ms, HR 100474.3 msQT / RR^(1/3)
FraminghamQT 400 ms, HR 100461.6 msQT + 154 × (1 − RR)
HodgesQT 400 ms, HR 100470.0 msQT + 1.75 × (HR − 60)

QTc interpretation needs a clinician and an ECG review. Formula choice can materially change a result, especially at higher heart rates.

Frequently Asked Questions about the QTc Calculator

What is the QTc interval?
The QT interval on an ECG measures ventricular depolarization and repolarization. Because QT shortens at high heart rates and lengthens at low ones, clinicians correct it (QTc) so values are comparable across heart rates. Long QTc is associated with dangerous arrhythmias like torsades de pointes.
Which formula should I use?
Bazett (QTc = QT / sqrt(RR)) is most common but overcorrects at high heart rates and undercorrects at low ones. Fridericia (cube root) is more accurate across heart rate ranges and preferred in research. Framingham and Hodges use linear corrections. The calculator shows all four for comparison.
What is the upper limit of normal QTc?
This site uses one threshold model across both QT calculators: QTc above 450 ms in men or above 460 ms in women is prolonged, and QTc above 500 ms is a high-risk result that needs urgent clinical review. Values above 440 ms but not above the sex-specific threshold are shown as borderline or upper-normal. These thresholds are screening cutoffs, not a diagnosis by themselves.
What causes a prolonged QTc?
Common causes include certain antiarrhythmics, antipsychotics, antibiotics (macrolides, fluoroquinolones), antifungals, methadone, low potassium or magnesium, congenital long QT syndrome, and bradycardia. Always check the CredibleMeds list before adding a QT-prolonging drug.
Is this a medical diagnosis?
No. This calculator is educational. Real-world interpretation requires the full ECG (rhythm, morphology, U waves) and clinical context. Bring concerning QTc values to a clinician.

Related Calculators

More calculators in "Health"

Treadmill Pace CalculatorTarget Heart Rate CalculatorIV Drip Rate CalculatorCorrected Calcium CalculatorWeight Loss Percentage CalculatorWeight Gain Calculator
See all 103 calculators in "Health"