Bazett QTc Calculator
Calculate corrected QT (QTc) quickly using Bazett’s formula. Enter a measured QT interval and either heart rate (bpm) or RR interval (seconds).
What is QTc and why does it matter?
The QT interval represents the time from ventricular depolarization to repolarization on an ECG. Because QT naturally changes with heart rate, clinicians often use a corrected value called QTc so readings can be compared more fairly across different rates.
A prolonged QTc can indicate increased risk for ventricular arrhythmias such as torsades de pointes. A very short QTc can also be clinically relevant. QTc is one piece of the puzzle—history, medications, electrolytes, and the full ECG all matter.
Bazett formula
Bazett’s equation is the most widely taught correction:
QTc = QT / √RR
- QT in milliseconds (ms)
- RR in seconds (s)
- If you enter heart rate, RR is calculated as 60 / HR
This calculator performs those steps for you and gives a quick interpretation band.
How to use this calculator
- Enter the measured QT interval from the ECG (in ms).
- Choose whether you want to enter heart rate or RR interval.
- Enter the second value.
- Choose interpretation profile (general, male, or female).
- Click Calculate QTc.
Example
If QT = 420 ms and heart rate = 75 bpm, RR = 60/75 = 0.8 s. Bazett QTc = 420 / √0.8 = about 469.6 ms.
Interpreting QTc ranges (quick reference)
Cutoffs vary slightly by source and clinical setting. A practical bedside approach is:
- General profile: normal roughly 360–440 ms, borderline 441–460 ms, prolonged >460 ms
- Male profile: normal roughly 350–430 ms, borderline 431–450 ms, prolonged >450 ms
- Female profile: normal roughly 360–450 ms, borderline 451–470 ms, prolonged >470 ms
Values that are markedly prolonged (for example, ≥500 ms) often receive urgent attention because arrhythmic risk rises.
Limitations of Bazett’s correction
Bazett is popular because it is simple, but it is not perfect:
- Can over-correct at higher heart rates
- Can under-correct at lower heart rates
- Less reliable in tachycardia or bradycardia extremes
Other correction formulas
Clinicians may also use Fridericia, Framingham, or Hodges formulas, especially when rate is far from normal.
Common causes of prolonged QTc
- Medication effects (certain antiarrhythmics, antibiotics, antipsychotics, and others)
- Electrolyte abnormalities (low potassium, magnesium, or calcium)
- Congenital long QT syndromes
- Structural heart disease, ischemia, or myocarditis
- Endocrine and metabolic disturbances
Always review the full medication list, including over-the-counter and supplement products.
Frequently asked questions
Is QTc alone enough to diagnose long QT syndrome?
No. Diagnosis typically uses ECG patterns over time, symptoms, family history, and sometimes genetic testing.
Can I use this as medical advice?
No. This is an educational calculator. Clinical decisions should be made by a licensed professional.
What if I only have RR in milliseconds?
Convert to seconds first: RR(seconds) = RR(ms) / 1000.
Does a normal QTc guarantee no risk?
Unfortunately not. A normal QTc lowers concern for prolonged-QT-related risk but does not replace full clinical evaluation.
Bottom line
This Bazett QTc calculator is a quick way to estimate corrected QT from common ECG inputs. It is useful for screening and learning, but interpretation should always be combined with patient context, repeat ECG review, and professional clinical judgment.