Corrected QT Interval (QTc) Calculator

Methodology

Bazett (1920), Fridericia (1920), Framingham (Sagie 1992), Hodges (1983)

RR = 60/HR (s); Bazett QT/√RR; Fridericia QT/∛RR; Framingham QT + 154(1 − RR); Hodges QT + 1.75(HR − 60)

AHA/ACCF/HRS recommend linear regression-based corrections rather than Bazett. Thresholds commonly used for a prolonged QTc are 450 ms in men and 460 ms in women.

Who it is for

Adults in sinus rhythm; measured QT interval.

Version

1.0.1

How this calculator works

Where the formula comes from

• Bazett (1920) divided QT by the square root of the RR interval; his correction was based on observations in only 39 young subjects.^[1][2]
• Fridericia (1920) proposed dividing QT by the cube root of the RR interval.^[3]
• The Framingham linear correction was derived from baseline ECGs of 5,018 Framingham Heart Study participants (2,239 men and 2,779 women), after excluding participants with coronary heart disease.^[2]

The inputs

• QT is measured from the start of the QRS complex to the end of the T wave; RR in seconds is 60 divided by the heart rate in beats per minute.^[1]
• The Framingham formula is QTc = QT + 0.154 × (1 − RR) with times in seconds, equivalent to QT + 154 × (1 − RR) with QT in milliseconds; Hodges adds 1.75 ms for every beat per minute above 60.^[2][4]

Versions and alternatives

• In the population studied, a 2016 comparison found Fridericia and Framingham performed better than Bazett for the outcomes assessed, including prediction of mortality.^[4]

Where accuracy falls (published evidence)

• Bazett's formula over-corrects QT at fast heart rates and under-corrects it at slow heart rates.^[2][5]
• The AHA/ACCF/HRS statement advises against rate correction when RR intervals vary widely, as in atrial fibrillation, or when the end of the T wave cannot be identified reliably.^[1]
• In ventricular conduction delays such as bundle branch block, a wide QRS lengthens the QT, so adjustment for QRS duration or use of the JT interval may be needed.^[1]

What guidelines say

• The 2009 AHA/ACCF/HRS statement recommends linear regression functions rather than Bazett's formula for rate correction.^[1]
• The 2009 AHA/ACCF/HRS statement gives a QTc of 460 ms or longer in adult women and longer than 450 ms in adult men as practical limits for a prolonged QT.^[1]
• It also recommends stating which correction method was used in ECG reports.^[1]
• AHA guidance recommends measuring QT in the lead with the longest QT; when T and U waves cannot be separated reliably, leads without superimposed U waves should be considered.^[6]

Sources

1. Rautaharju PM, Surawicz B, Gettes LS, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241–e250. doi:10.1161/CIRCULATIONAHA.108.191096
2. Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol. 1992;70(7):797–801. doi:10.1016/0002-9149(92)90562-D
3. Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469–486. doi:10.1111/j.0954-6820.1920.tb18266.x
4. Vandenberk B, Vandael E, Robyns T, et al. Which QT correction formulae to use for QT monitoring? J Am Heart Assoc. 2016;5(6):e003264. doi:10.1161/JAHA.116.003264
5. Funck-Brentano C, Jaillon P. Rate-corrected QT interval: techniques and limitations. Am J Cardiol. 1993;72(6):17B–22B. doi:10.1016/0002-9149(93)90035-B
6. Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation. 2010;121(8):1047–1060. doi:10.1161/CIRCULATIONAHA.109.192704

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on 2026-10-11

Worked example: how to calculate QTc

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

• Not reliable in atrial fibrillation, bundle branch block or with paced rhythms without adjustment.
• Measure QT in the lead with the longest QT, ideally averaged over several beats.

References

1. Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241–e250. doi:10.1161/CIRCULATIONAHA.108.191096
2. Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353–370.
3. Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand. 1920;53:469–486.
4. Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol. 1992;70(7):797–801. doi:10.1016/0002-9149(92)90562-D
5. Hodges M, Salerno D, Erlien D. Bazett's QT correction reviewed: evidence that a linear QT correction for heart rate is better. J Am Coll Cardiol. 1983;1:694.