QTc Fridericia, Framingham and Hodges Calculator

The three corrections that behave better than Bazett, on one trace at once. Fridericia is the headline because ICH E14 calls it the more accurate of the pair it requires; the other three sit beside it so the disagreement is visible.

Last updated 8 Oct 2026

Fridericia QTc, with Framingham and Hodges

4 corrections, 1 trace

Measured QT interval (ms)Earliest QRS onset to latest T-wave offset, in the lead where the QT is longest (usually II, V5 or V6), by the tangent method. Do not include a U wave; where T and U merge the measurement is unreliable and so is everything below it.

Heart rate or RR intervalFrom the beat the QT was measured on.

Rate unitSet the unit to match what you are holding. Every rate correction here was published with RR in SECONDS, so a heart rate typed into an RR field is the commonest way these formulas are got wrong: at 100 bpm it divides the QT by 10 instead of by 0.775. Both quantities are printed back under the answer.

474ms (Fridericia)Example

QT 400 ms, heart rate 100 bpm

The four corrections

Fridericia QTc = QT / RR^1/3
Framingham QTc = QT + 154 × (1 − RR)
Hodges QTc = QT + 1.75 × (HR − 60)
Bazett QTc = QT / RR^1/2
QT in ms, RR in seconds, HR in bpm

Fridericia, 1920: the cube root rather than the square root, published the same year as Bazett’s and ignored for most of a century. ICH E14 calls it “more accurate than Bazett’s correction in subjects with such altered heart rates” and requires both in any submission
Framingham, 1992: a linear correction from the Framingham Heart Study, published as QT + 0.154 × (1 − RR) with QT in seconds, which is QT + 154 × (1 − RR) in milliseconds. Strong at fast rates, weakest of the four at slow ones — at 40 bpm it sits 26 ms below Fridericia
Hodges, 1983: the only one written in heart rate rather than RR interval: add 1.75 ms per beat per minute above 60. The Clinical Cardiology 2020 bundle-branch-block study found Hodges the best rate correction to pair with the Bogossian wide-QRS adjustment
the threshold problem: the published 450, 460 and 500 ms figures were derived on Bazett-corrected data, so reading a Fridericia value against them is an approximation — close at ordinary rates, not close at 120 bpm. That is the honest reason Bazett has not been retired

Worked example

QT 400 ms, heart rate 100 bpm
RR = 60 / 100 = 0.600 s
Fridericia: 400 / 0.600^1/3 = 400 / 0.8434 = 474 ms
Framingham: 400 + 154 × (1 − 0.600) = 462 ms
Hodges: 400 + 1.75 × (100 − 60) = 470 ms; Bazett: 400 / √0.600 = 516 ms
Three of the four cluster within 12 ms; Bazett sits 42 ms above the nearest. The 55 ms spread straddles ICH E14's 500 ms threshold of particular concern
At 150 bpm the same QT gives 632, 543, 492 and 558 ms — a 140 ms spread, a third of the measurement being corrected

One 400 ms QT, four corrections, seven heart rates

This calculator’s own arithmetic on one unchanged measurement. The spread column is the point: zero at 60 bpm, 55 ms at 100, 140 ms at 150. A 140 ms disagreement is wider than the whole distance between a normal QTc and the 500 ms concern threshold, and it comes from the choice of formula alone.
Heart rate (bpm)	Bazett (ms)	Fridericia (ms)	Framingham (ms)	Hodges (ms)	Spread (ms)
40	327	349	323	365	42
50	365	376	369	382	17
60	400	400	400	400	0
80	462	440	438	435	27
100	516	474	462	470	55
120	566	504	477	505	89
150	632	543	492	558	140

What each correction is, and what it is recommended for

None of the four original papers was reachable from this environment. The algebra of all four was taken from two independent reproductions that agree character for character, and Bazett’s and Fridericia’s are quoted in the ICH E14 text, which was read in full. These citations are the formulas’ sources, not documents consulted here.
Correction	Published form	Source	Where it is used
Bazett	QT / RR^(1/2)	Bazett, Heart 1920;7:353	ECG carts, drug labels, historical datasets, almost every published threshold
Fridericia	QT / RR^(1/3)	Fridericia, Acta Med Scand 1920;53:469	Regulatory QT assessment; ICH E14 calls it more accurate at altered rates and requires it alongside Bazett
Framingham	QT + 0.154 × (1 − RR), QT in seconds	Sagie et al, Am J Cardiol 1992;70:797	Epidemiology; strong at fast rates, weakest of the four at slow ones
Hodges	QT + 1.75 × (HR − 60)	Hodges et al, J Am Coll Cardiol 1983;1:694	Paired with the Bogossian adjustment for a wide QRS, where it gave the closest agreement with the narrow-QRS QTc

Three better corrections, and the thresholds they borrow

All four rate corrections in common use answer the same question — what would this QT have been at 60 beats per minute — and answer it differently, because each is a different curve fitted to a different cohort. Fridericia divides by the cube root of the RR interval. Framingham and Hodges are linear: Framingham adds 154 ms per second of RR shortening, Hodges 1.75 ms per beat per minute above 60. Bazett divides by the square root. At 60 bpm, where RR is exactly one second, all four return the measured QT and agree perfectly. Everywhere else they separate, and the separation is large.

How large is the content of this page. On one unchanged 400 ms measurement the four span 27 ms at 80 bpm, 55 ms at 100, 89 ms at 120 and 140 ms at 150. Below 60 bpm the ordering reverses and Framingham becomes the outlier: at 40 bpm it returns 323 ms where Hodges returns 365. So no formula is simply right. What the published comparisons agree on is narrower and more useful — the residual dependence on heart rate, the thing a correction exists to remove, is smallest for Fridericia across most cohorts, which is why ICH E14 singles it out and why the regulatory literature on drug-induced QT prolongation moved towards it.

The awkwardness is that the thresholds did not move with it. The 450 and 460 ms upper limits, and ICH E14’s own 500 ms concern threshold, were derived on Bazett-corrected data. A Fridericia value read against them is an approximation: at resting rates a very close one, at 120 bpm not close at all. That is the honest reason Bazett survives, and why ICH E14 asks for both rather than choosing.

The practical reading is comparative. Where the four values beside the answer cluster, the heart rate is not doing much work and a long QTc means a long QT. Where Bazett stands well above the other three, the rate is driving the result and the correction deserves more scepticism than the patient does. A large spread is itself a signal: it means the trace sits far from 60 bpm, where every correction is on its least reliable ground. None of the four applies unaltered to a QRS of 120 ms or more; that needs the wide-QRS adjustment. This supports a clinician’s judgement rather than replacing it. An ECG interval is read alongside the patient, the drug chart and the electrolytes, and never instead of them.

Frequently asked questions

What is Fridericia’s QTc formula?

QTc = QT divided by the cube root of the RR interval in seconds. At 100 bpm the RR interval is 0.6 s, its cube root 0.8434, so a measured QT of 400 ms corrects to 474 ms — against 516 ms by Bazett on the same trace.

Is Fridericia better than Bazett?

ICH E14 says it is “more accurate than Bazett’s correction in subjects with such altered heart rates” and requires both in a drug submission. In published comparisons Fridericia leaves the least residual dependence on heart rate. The caveat is that the familiar thresholds were derived on Bazett-corrected data.

What is the Framingham QT correction?

A linear correction from the Framingham Heart Study: QTc = QT + 0.154 × (1 − RR) with QT in seconds, which is QT + 154 × (1 − RR) in milliseconds. It behaves well at fast rates and is the weakest of the four at slow ones — at 40 bpm it sits 26 ms below Fridericia on the same trace.

How different are the QTc formulas in practice?

On one unchanged 400 ms QT they differ by 0 ms at 60 bpm, 27 ms at 80, 55 ms at 100, 89 ms at 120 and 140 ms at 150. Those are this page’s own figures, and the 120 bpm case straddles ICH E14’s 500 ms threshold of particular concern.

Which correction should be used with a wide QRS?

None on its own. A QRS of 120 ms or more inflates the QT without lengthening repolarisation, so the wide QRS has to be accounted for first. The Clinical Cardiology 2020 bifascicular-block study found the Bogossian modified QT with the Hodges correction agreed most closely with the narrow-QRS QTc.

Related calculators

References

International Council for Harmonisation. E14 Clinical Evaluation of QT/QTc Interval Prolongation and Proarrhythmic Potential for Non-Antiarrhythmic Drugs. Guidance for industry, US Food and Drug Administration, October 2005.
Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Medica Scandinavica. 1920;53:469–486.
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.
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 (abstract).

Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/