What is the QTc?
Enter the QT interval and the heart rate (or RR interval) from an ECG to get the corrected QT (QTc) by four formulas. For information only. This is not medical advice or a diagnosis. Do not use it to make treatment decisions without a clinician. No licensed clinician has reviewed this page.
- QTc
- 447
The Bazett QTc is 447 ms: Normal range.
- Reading
- Normal range
- Bazett
- 447
- Fridericia
- 431
- Framingham
- 431
- Hodges
- 426
- Heart rate
- 75
QTc: 447. The Bazett QTc is 447 ms: Normal range.
QTc by qT interval (ms)
This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use
How to calculate
Corrects the QT interval of an ECG for heart rate with the Bazett, Fridericia, Framingham, and Hodges formulas, and reads the result with the AHA/ACCF/HRS cut-offs for men and women.
Example with the default inputs (QT interval (ms) 400, Rate given as Heart rate, Heart rate (beats/min) 75, Headline formula Bazett, Sex Male): The Bazett QTc is 447 ms: Normal range.
Method: RR (s) = 60 ÷ heart rate. Bazett: QT ÷ √RR. Fridericia: QT ÷ ∛RR. Framingham: QT + 154 × (1 − RR). Hodges: QT + 1.75 × (heart rate − 60). QT in ms.
- A regular rhythm; each QTc is rounded to a whole millisecond and the reading uses the headline value.
- Long QTc: 450 ms or more in men, 460 ms or more in women; short: 390 ms or less (AHA/ACCF/HRS 2009). Over 500 ms is shown separately (Drew 2010, AHA/ACCF statement on torsade de pointes: highly abnormal).
Worked examples
Each example is checked against the calculator on every build.
- QT interval (ms) 400, Rate given as Heart rate, Heart rate (beats/min) 75, Headline formula Bazett, Sex Male gives QTc 447, Reading Normal range, Bazett 447, Fridericia 431, Framingham 431, Hodges 426.Source: Bazett 1920: 400 ÷ √0.8 = 447.2; Fridericia 1920: 400 ÷ ∛0.8 = 430.9; Sagie 1992: 400 + 154 × 0.2 = 430.8; Hodges 1983: 400 + 1.75 × 15 = 426.25
- QT interval (ms) 400, Rate given as Heart rate, Heart rate (beats/min) 60, Headline formula Fridericia, Sex Female gives QTc 400, Bazett 400, Fridericia 400, Framingham 400, Hodges 400.
- QT interval (ms) 360, Rate given as RR interval, RR interval (ms) 600, Headline formula Bazett, Sex Female gives QTc 465, Reading Long: 460 ms or more, Fridericia 427, Framingham 422, Hodges 430.
- QT interval (ms) 480, Rate given as Heart rate, Heart rate (beats/min) 90, Headline formula Hodges, Sex Male gives QTc 533, Reading Long: over 500 ms, Bazett 588.
Medical disclaimer
This calculator is for information and education only. It is not medical advice, and its result is not a diagnosis. Do not use it to start, stop, or change a treatment without a clinician who knows your health history. No licensed clinician has reviewed this page. This site's editors checked the formulas and worked examples against published sources. If you think you have a medical emergency, call your local emergency number.
When this does not apply. The cut-offs are for adults (Rautaharju 2009). A single-beat QTc is not reliable with an irregular rhythm such as atrial fibrillation, and a wide QRS (for example bundle branch block) lengthens the QT for another reason.
How the QTc is worked out
QT is in milliseconds (ms). RR is the RR interval in seconds: RR = 60 ÷ heart rate, or the RR interval in ms ÷ 1,000. The heart rate from an RR interval is 60 ÷ RR.
| Formula | QTc (ms) |
|---|---|
| Bazett (1920) | QT ÷ √RR |
| Fridericia (1920) | QT ÷ ∛RR |
| Framingham (Sagie 1992) | QT + 154 × (1 − RR) |
| Hodges (1983) | QT + 1.75 × (heart rate − 60) |
Each QTc is rounded to a whole millisecond (halves round up, read from the decimal value: a result within 1e-9 (relative) of a half counts as the half, so 2.005 rounds to 2.01). The headline shows the formula you pick; the page lists all four. The QT must be shorter than the RR interval.
Reading
Read from the headline QTc, with the AHA/ACCF/HRS 2009 cut-offs and the 500 ms level of the 2010 AHA/ACCF statement (Drew 2010: a QTc over 500 ms is highly abnormal):
| QTc | Reading |
|---|---|
| over 500 ms | Long: over 500 ms |
| 450 ms or more (men), 460 ms or more (women) | Long |
| 390 ms or less | Short |
| otherwise | Normal range |
Inputs the calculator accepts
QT 200 to 700 ms, heart rate 30 to 250 beats per minute, RR 240 to 2,000 ms.
The chart draws the QTc for a QT from 300 to 500 ms at the rate you entered, as a heart rate or as an RR interval.
Worked examples by hand
The default. QT 400 ms at 75 beats/min, so RR = 0.8 s. Bazett = 400 ÷ 0.89443 = 447.2, shown as 447. Fridericia = 400 ÷ 0.92832 = 431. Framingham = 400 + 154 × 0.2 = 431. Hodges = 400 + 1.75 × 15 = 426.25, shown as 426. For a man, 447 is under 450: normal range.
At 60 beats/min. RR = 1 s, so every formula returns the QT: 400 ms.
RR 600 ms, woman. QT 360 ms, RR = 0.6 s (100 beats/min). Bazett = 360 ÷ 0.77460 = 465 (long for a woman, 460 or more). Fridericia = 360 ÷ 0.84343 = 427. Framingham = 360 + 154 × 0.4 = 422. Hodges = 360 + 1.75 × 40 = 430. Bazett reads long while the others do not, which shows its over-correction at fast rates.
Hodges, man. QT 480 ms at 90 beats/min: Hodges = 480 + 1.75 × 30 = 532.5, shown as 533, long (over 500 ms). Bazett = 480 ÷ √(0.6667) = 588.
Other questions people ask
What is the QTc?
The QT interval is the time on an ECG from the start of the Q wave to the end of the T wave: how long the heart muscle takes to recharge after each beat. It gets shorter as the heart rate rises, so it is "corrected" to what it would be at 60 beats per minute. That corrected value is the QTc.
What is a normal QTc?
The 2009 AHA/ACCF/HRS recommendations call a QTc of 450 ms or more long in men and 460 ms or more long in women, and 390 ms or less short. The 2010 AHA/ACCF statement calls a QTc over 500 ms highly abnormal: it goes with a 2 to 3 times higher risk of a dangerous rhythm called torsade de pointes.
Which QTc formula is best?
Bazett (1920) is the most used, but it over-corrects at fast heart rates and under-corrects at slow ones. Fridericia, Framingham, and Hodges change less with heart rate, and the AHA/ACCF/HRS recommendations prefer a linear formula such as Framingham or Hodges. The page shows all four so you can compare them.
What is the RR interval?
The time between two R waves on the ECG, the time of one heartbeat. RR in seconds is 60 divided by the heart rate: at 75 beats per minute, RR is 0.8 seconds (800 ms).
Can I use the QTc with atrial fibrillation or a wide QRS?
With an irregular rhythm the RR changes from beat to beat, so the QTc from one beat is not reliable; clinicians average several beats. A wide QRS (for example bundle branch block) lengthens the QT for another reason and needs a different approach.