QTc Rechner (Corrected QT Calculator)
Use this tool to estimate corrected QT (QTc) from a measured QT interval and heart rate. It calculates common formulas used in ECG interpretation: Bazett, Fridericia, Framingham, and Hodges.
- Bazett: QTc = QT / √RR
- Fridericia: QTc = QT / RR1/3
- Framingham: QTc = QT + 0.154 × (1 − RR)
- Hodges: QTc = QT + 1.75 × (HR − 60)
Educational use only. This calculator does not replace clinical judgment or a physician's interpretation.
What is a QTc Rechner?
A QTc Rechner is a calculator used to estimate the corrected QT interval (QTc) on an electrocardiogram (ECG). The raw QT interval changes with heart rate, so clinicians use correction formulas to compare values more fairly across fast or slow rhythms.
Why QTc matters in practice
A prolonged QTc can be associated with increased risk of ventricular arrhythmias, including torsades de pointes. A shortened QTc can also be clinically relevant in selected cases. Because medications, electrolyte shifts, structural heart disease, and congenital syndromes can influence QT, consistent calculation is important.
- Drug safety checks (for example, before and during QT-prolonging medication)
- Evaluation of syncope, palpitations, or arrhythmia risk
- Monitoring in electrolyte disturbances (e.g., hypokalemia, hypomagnesemia)
- Assessment in inherited channelopathies
How to use this calculator
Step 1: Enter measured QT
Use the QT interval from your ECG in milliseconds (ms). Ensure your measurement is from a clean tracing and representative beat.
Step 2: Enter heart rate
Provide heart rate in beats per minute (bpm). The tool automatically converts this to RR interval for formulas that use RR.
Step 3: Choose formula display
You can display all formulas at once, or focus on one method. Different formulas perform differently at very high or very low heart rates.
Quick interpretation guide
Interpretation varies by context, but common reference points are:
| Group | Generally Normal | Borderline | Prolonged |
|---|---|---|---|
| Men | < 450 ms | 450–469 ms | ≥ 470 ms |
| Women | < 460 ms | 460–479 ms | ≥ 480 ms |
Many clinicians use 500 ms as a high-risk threshold, especially if QTc is rising over time or other risk factors are present.
Formula notes: which QT correction is best?
Bazett formula
Historically the most common. It tends to overcorrect at high heart rates and undercorrect at low heart rates.
Fridericia formula
Often preferred in drug safety and research settings because it behaves better across broader heart-rate ranges.
Framingham and Hodges
Linear correction formulas that can provide useful alternatives in clinical review, particularly when Bazett appears extreme.
Important limitations
- QT measurement itself can vary based on lead choice and T-wave morphology.
- U waves, bundle branch block, pacing, and atrial fibrillation can complicate interpretation.
- Clinical decisions should include symptoms, trend, medication profile, and lab data.
Bottom line
This QTc Rechner gives a fast way to estimate corrected QT using several established formulas. Use it to support ECG review, compare correction methods, and improve consistency. For medical decisions, always combine calculator output with full clinical assessment.