For healthcare professionals
QTc Calculator
The QT interval on an electrocardiogram (ECG) gets shorter as the heart rate rises, so it is corrected for heart rate before it is compared with a limit. Different formulas give different answers, especially at fast or slow heart rates. This tool shows the four common ones side by side. It is written for clinicians and is not a diagnosis.
ECG values
Use the QT interval and heart rate from the same ECG. Nothing you enter leaves this page.
What you will see
The QTc by each of the four formulas, and whether each is above the limit for the sex you chose.
Educational only, not medical advice. Not a diagnosis. Decisions belong to the treating team.
Source
The four formulas (Table 1) and the QTc cut-offs as printed by Rosenblum AL and colleagues, Cureus 2020, an open-access (CC BY) study. The tests check that all four formulas return the measured QT at 60 beats per minute, each formula at a fast and a slow rate, that a value equal to a limit is not called prolonged, and that a value is never displayed as a limit it is not.
Validated in
Rosenblum 2020 studied 44,566 ECGs from one year at a single US tertiary care center: heart rate 60 to 120 beats per minute, QRS duration not over 120 ms, mean age 57, 57% female.
Limits
No single formula is agreed to replace Bazett. Bazett becomes less reliable as the heart rate rises above or falls below 60 beats per minute. The study did not include ECGs with a wide QRS (over 120 ms) or a heart rate outside 60 to 120. Table 1 does not print units: the tool works Bazett, Fridericia and Framingham in seconds (RR = 60 / heart rate) and Hodges in milliseconds, then shows every result in milliseconds.
The formulas
As printed in Table 1 of Rosenblum 2020, with RR the interval between beats and HR the heart rate (Rosenblum 2020):
- Bazett: QTc = QT / square root of RR.
- Fridericia: QTc = QT / cube root of RR.
- Framingham: QTc = QT + 0.154 x (1 - RR).
- Hodges: QTc = QT + 1.75 x (HR - 60).
Worked example: a QT of 360 ms at 100 beats per minute (RR 0.6 s) gives 464.8 ms by Bazett, 426.8 ms by Fridericia, 421.6 ms by Framingham and 430 ms by Hodges. At 60 beats per minute (RR 1 s) all four give the measured QT.
The cut-offs
The study counted a QTc as prolonged above 450 ms in males and above 460 ms in females, and looked separately at a QTc over 500 ms. It describes a normal QTc as 350 to 450 ms in males and 350 to 460 ms in females, and notes that the risk of torsades de pointes rises as the Bazett QTc goes above 500 ms (Rosenblum 2020). The tool marks a value as above a limit only when it is greater than the limit, not equal to it.
What the study found
Across 44,566 ECGs with a mean heart rate of 83 beats per minute, the Fridericia QTc was a mean 23 ms shorter than the Bazett QTc. Bazett called 37.4% of the ECGs prolonged; with Fridericia, 21% of all the ECGs moved to a normal QTc, and the number over 500 ms fell by 57.3%. The authors note that American Heart Association, American College of Cardiology Foundation and Heart Rhythm Society guidance has recommended formulas other than Bazett since 2009, and that guidance asks for the formula to be named with each QTc (Rosenblum 2020).
Related tools
For whether an ECG is advised in people without symptoms, see the ECG screening check. To adjust total calcium for a low albumin, see the corrected calcium calculator. Other bedside scores are listed under For healthcare professionals.
Sources
- Rosenblum AL, Dremonas AC, Stockholm SC, Biondi NL. A retrospective analysis of hospital electrocardiogram auto-populated QT interval calculation. Cureus. 2020;12(7):e9317. doi:10.7759/cureus.9317. PMID 32714713. Open access (CC BY). Table 1 (Bazett, Fridericia, Framingham and Hodges formulas), Introduction and Abstract (QTc cut-offs 450 ms male, 460 ms female, 500 ms; 44,566 ECGs). pmc.ncbi.nlm.nih.gov/articles/PMC7376804/
Written and maintained by the uncovermyrisk.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-11-02. Spotted an error? See About.