Corrects the QT interval for heart rate with the Bazett, Fridericia, Framingham or Hodges formula, and shows where the result falls against the adult limits.
Result
Enter the QT interval and the heart rate or RR interval.
Sources
4 studies
4
studies
832
citations
13,470
PubMed papers
Evidence
Known limitations
The AHA/ACCF/HRS recommendations on the QT interval set prolonged QTc at 450 ms or more in men and 460 ms or more in women, and short at 390 ms or less, and recommend a linear correction over Bazett.
Circulation: Journal Metrics Score 2.3, Q2 · cited 434 times
In 6,609 patients, Fridericia and Framingham corrected best for heart rate and predicted 30-day and 1-year mortality better than Bazett, which identified many more patients as prolonged.
J Am Heart Assoc: Journal Metrics Score 5.3, Q1 · cited 434 times
PubMed · Free full text · DOI
The AHA/ACCF statement on preventing torsade de pointes in hospital treats a QTc above 500 ms, or a rise of 60 ms or more from the pre-drug baseline, as a marker of high risk.
Circulation: Journal Metrics Score 2.3, Q2 · cited 844 times
PubMed · Free full text · DOI
Among 5,018 Framingham participants, a linear correction adjusted the QT for heart rate more reliably than Bazett, which overcorrected at fast rates and undercorrected at slow ones.
Am J Cardiol: Journal Metrics Score 2.2, Q2 · cited 718 times
The original paper has been cited 832 times, and 13,470 PubMed articles mention the corrected QT interval in their title or abstract. Citation counts from OpenAlex and article counts from PubMed, retrieved November 12, 2026. Journal Metrics Scores and quartiles are from this site’s current release; follow the journal name for details.
After the result
QTc above 500 ms · Prolonged QTc · Any result
High risk of torsade de pointes. Look for a cause. Use one formula consistently.
Next steps
Avoid common errors
5 common errors to avoid
and 3 more
When the QTc misleads
1Fast or slow heart rate
Bazett overcorrects above about 85 per minute, making normal QT intervals look prolonged, and undercorrects in bradycardia. Fridericia or Framingham are less affected.
2Wide QRS
Bundle branch block, ventricular pacing and pre-excitation lengthen the QT without a change in repolarization; the usual thresholds then overstate the risk.
3Atrial fibrillation
The RR interval varies from beat to beat. Average the QT and RR over several beats instead of using a single one.
4Automated readings
ECG machines measure the QT differently and can include U waves or miss a flat T wave end. Check a borderline machine reading by hand.
5Children and newborns
Normal limits differ in children and newborns; the adult thresholds on this page do not apply to them.
Formula
Bazett QTc = QT / √RR; Fridericia QT / ∛RR; Framingham QT + 154 × (1 − RR); Hodges QT + 1.75 × (heart rate − 60).
QTc = QT / √RR
Bazett QTc = QT / √RR; Fridericia QT / ∛RR; Framingham QT + 154 × (1 − RR); Hodges QT + 1.75 × (heart rate − 60).
Formulas and normal ranges
| Formula | QTc | Note |
|---|---|---|
| Bazett | QT / √RR | The most widely used; overcorrects at fast heart rates and undercorrects at slow ones. |
| Fridericia | QT / ∛RR | Cube root of RR; less dependent on heart rate than Bazett. |
| Framingham | QT + 154 × (1 − RR) | Linear correction from 5,018 Framingham participants (Sagie 1992). |
| Hodges | QT + 1.75 × (HR − 60) | Linear correction by heart rate (Hodges 1983, published as a meeting abstract). |
| RR interval | 60 / heart rate | In seconds; 1 s at a heart rate of 60, where every formula gives QTc = QT. |
| Range | QTc (ms) | Meaning |
|---|---|---|
| Short | ≤ 390 | Short QTc. A value of 390 ms or less is below the usual range; a QTc of 360 ms or less with unexplained syncope, cardiac arrest, or a family history of sudden death or short QT syndrome raises the question of short QT syndrome. |
| Normal | 391 to 449 (men), 391 to 459 (women) | Within the usual adult range. |
| Prolonged | 450 to 500 (men), 460 to 500 (women) | Prolonged QTc. Review QT-prolonging drugs, potassium, magnesium and calcium, and consider an inherited long QT syndrome. |
| High risk | > 500 | A QTc above 500 ms is associated with a substantially higher risk of torsade de pointes (Drew 2010). |
Bazett 1920
Fridericia 1920
Framingham 1992
Test cases
3 published cases, each also a test case
3 published cases; the calculator reproduces every result.
Worked examples
A 39-year-old man whose smartwatch ECG showed a long QT had a 12-lead ECG with a QT of 540 ms at a heart rate of 56 per minute. The authors reported a Bazett QTc of 522 ms, and genetic testing confirmed congenital long QT syndrome.
At a heart rate below 60 the Bazett QTc is shorter than the measured QT. The paper reports a Framingham QTc of 528 ms; the 529 ms here comes from the rounded heart rate of 56.
Entered as: QT interval: 540 ms; Heart rate: 56 beats/min; Correction formula: Bazett; Sex: Male.
Source: Rudic B et al., HeartRhythm Case Rep 2024 (PubMed · Free full text · DOI)
A 67-year-old woman with gastric adenocarcinoma came to the emergency department on the fifth day of capecitabine-based chemotherapy with chest pain attributed to coronary vasospasm; QT prolongation followed after the regimen was restarted. Her first ECG, labelled baseline in the figure, showed a heart rate of 52 per minute and a QT of 466 ms, with a QTc of 434 ms by Bazett and 444 ms by Fridericia.
“Corrected QT Interval (QTc, Bazett) of 434 ms, and QTc (Fridericia) of 444 ms”
Choosing Bazett gives the 434 ms in the same figure legend. At slow rates Fridericia gives the higher value.
Entered as: QT interval: 466 ms; Heart rate: 52 beats/min; Correction formula: Fridericia; Sex: Female.
Source: Dominguez-Linares A et al., JACC Case Rep 2026 (PubMed · Free full text · DOI)
A female newborn with long QT syndrome type 3 had functional 2:1 atrioventricular block. Before a mexiletine challenge test her RR interval was 750 ms and her QT 464 ms, giving a QTc of 536 ms by Bazett and 511 ms by Fridericia.
“RR 750 ms, QT 464 ms, QTcB 536 ms, and QTcF 511 ms”
Entered with the RR interval instead of the heart rate. The adult thresholds do not apply to newborns; the example shows the arithmetic only.
Entered as: QT interval: 464 ms; RR interval: 750 ms; Correction formula: Bazett; Sex: Female.
Source: Okuwaki H et al., J Arrhythm 2019 (PubMed · Free full text · DOI)
FAQ
7 questions and answers
and 5 more answers
Questions
Divide the QT interval by the square root of the RR interval in seconds (Bazett): QTc = QT / √RR, where RR = 60 / heart rate. A QT of 400 ms at a heart rate of 75 (RR 0.8 s) gives 400 / 0.894 = 447 ms. Fridericia uses the cube root instead, and the Framingham and Hodges formulas add a linear correction.
The AHA/ACCF/HRS recommendations (Rautaharju 2009) treat a QTc of 450 ms or more in men and 460 ms or more in women as prolonged, and 390 ms or less as short. Above 500 ms the risk of torsade de pointes rises substantially (Drew 2010).
Bazett is the most widely used but overcorrects at fast heart rates and undercorrects at slow ones. In 6,609 patients, Vandenberk and colleagues (2016) found Fridericia and Framingham left the least residual dependence on heart rate and predicted 30-day and 1-year mortality better, and concluded that the routine use of Bazett for QT monitoring should be questioned. Whichever you use, use the same formula for repeated measurements in the same patient.
No formula removes the effect of heart rate completely. Bazett’s square root overcorrects: at a heart rate of 100 a normal QT of 360 ms becomes a Bazett QTc of 465 ms but a Fridericia QTc of 427 ms. Comparing formulas, or repeating the ECG at a slower rate, shows whether a borderline value is real.
A QTc above 500 ms, or a rise of 60 ms or more from the pre-drug baseline, is associated with a higher risk of torsade de pointes (Drew 2010). The risk is higher with low potassium or magnesium, slow heart rates, female sex, heart disease and several QT-prolonging drugs together.
Measure from the start of the QRS complex to the end of the T wave, usually in lead II or V5, where the T wave ends most clearly. Leave out a U wave that is separate from the T wave. Average a few beats, especially in atrial fibrillation, where the RR interval varies from beat to beat. Use the same lead for repeated measurements in the same patient.
A wide QRS lengthens the QT without any change in repolarization, so the usual thresholds overstate the risk. Several adjustments exist, such as subtracting the extra QRS width or using the JT interval, but none is part of these four formulas. Interpret the QTc with care when the QRS is 120 ms or wider.
Further reading
9 references with PubMed and DOI links
9
references
6
free full text
From Bazett HC, Ann Noninvasive Electrocardiol 1997 to the newest case reports.
References
Contributed by Dr. Meng Zhao (MD · Former Neurosurgeon · Medical AI Researcher), from the original publications listed here. Last updated November 12, 2026. LinkedIn
The calculator code is tested against every worked example on this page before each release.
This calculator supports, and does not replace, clinical judgment. It is meant for healthcare professionals and is not medical advice for patients. Report an error through the contact page.
clinical grade of aneurysmal subarachnoid hemorrhage, I to V.
total calcium adjusted for albumin, in mg/dL or mmol/L.
stroke severity from 15 bedside items, 0 to 42.
MAP from systolic and diastolic pressure, against the 65 mm Hg target.
eye, verbal and motor scores for preverbal children, 3 to 15.
oxygenation ratio with the Berlin ARDS severity ranges.
serum sodium corrected for high glucose, Katz or Hillier factor.
sodium − (chloride + bicarbonate), with the albumin-corrected gap.
urea nitrogen to creatinine ratio, in US or SI units.
estimated creatinine clearance with actual, ideal or adjusted weight.
cardiac output and index from oxygen consumption and saturations.
ANC from the white cell count, neutrophils and bands.
insulin resistance from fasting glucose and insulin, in US or SI units.
FENa from plasma and urine sodium and creatinine: prerenal, indeterminate or tubular pattern.
three-item stroke severity screen for large vessel occlusion, 0 to 4.
water deficit in hypernatremia from sodium, weight and body water.
expected PaCO2 in metabolic acidosis, 1.5 × HCO3 + 8 ± 2.
head CT decision rule for children with minor head trauma.
blood loss before hemoglobin or hematocrit reaches a chosen lowest value.
eye, verbal and motor response, 3 to 15, with GCS-Pupils.
Devine ideal body weight and adjusted weight from height and sex.
Another bedside cardiovascular calculation.
For cardiac output from oxygen consumption.
Which published the AHA/ACCF/HRS QT recommendations and the torsade statement, with its current metrics.