QTc calculator
Enter the QT interval and either the heart rate or the RR interval to get the corrected QT by four common formulas side by side. It is an estimate for information, not a diagnosis.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the QT interval in milliseconds.
- Choose whether you know the heart rate (bpm) or the RR interval (ms), and enter it.
- Read the corrected QT by each formula.
QT is in milliseconds, RR in seconds (RR = 60 ÷ heart rate), HR in beats per minute:
- Bazett: QTc = QT ÷ √RR
- Fridericia: QTc = QT ÷ ∛RR
- Framingham: QTc = QT + 154 × (1 − RR)
- Hodges: QTc = QT + 1.75 × (HR − 60)
Worked example
QT 400 ms at a heart rate of 75 bpm. RR = 60 ÷ 75 = 0.8 s.
- Bazett: 400 ÷ √0.8 = 400 ÷ 0.894 = 447 ms
- Fridericia: 400 ÷ ∛0.8 = 400 ÷ 0.928 = 431 ms
- Framingham: 400 + 154 × 0.2 = 431 ms
- Hodges: 400 + 1.75 × 15 = 426 ms
Tips and common mistakes
- Enter milliseconds, not seconds or small squares: 0.40 s is 400 ms.
- Measure QT and RR on the same beats. In atrial fibrillation the RR interval varies, so an average over several beats is used.
- At high heart rates the formulas disagree the most; Bazett gives the largest number there.
- This is an estimate for information, not a diagnosis. ECG interpretation belongs to a clinician.
Frequently asked questions
Which QTc formula should I use?
Bazett is the oldest and most widely printed by ECG machines, but it overcorrects at fast heart rates and undercorrects at slow ones. Fridericia and Framingham behave better away from 60 bpm, and many drug-safety studies use Fridericia. Compare them side by side here.
What QTc is considered prolonged?
Thresholds differ by source and by sex. Values above about 450 ms in men and 460–470 ms in women are often called prolonged, and above 500 ms is commonly treated as high risk. Your clinician decides what applies.
How do I get the RR interval from the heart rate?
RR in seconds = 60 ÷ heart rate in beats per minute. At 75 bpm the RR interval is 0.8 s, or 800 ms. The calculator shows whichever of the two you did not enter.
Why do all four formulas give the same number at 60 bpm?
At 60 bpm the RR interval is exactly 1 second, which is the reference point of every formula, so no correction is applied.