# QTc Calculator (Corrected QT Interval)

URL: https://speedycalculator.com/calculators/health/qtc/
Last updated: 2026-10-25

> The QTc calculator corrects the QT interval on an ECG for heart rate using the Bazett, Fridericia and Framingham formulas. A QTc above about 450 ms in men or 460 ms in women is generally considered prolonged.

## Inputs

- QT interval (ms)
- Heart rate (bpm)

## Results

- RR interval
- QTc (Bazett)
- QTc (Fridericia)
- QTc (Framingham)

## Formula

```
RR = 60 ÷ HR (s)
Bazett: QTc = QT ÷ √RR
Fridericia: QTc = QT ÷ ∛RR
Framingham: QTc = QT + 154 × (1 − RR)
```

## Explanation

The QT interval shortens as heart rate rises, so it must be corrected before comparing it with normal limits.

### How to use the QTc Calculator

- **QT interval**
- **Heart rate**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Convert heart rate to the RR interval in seconds and apply each correction formula.

### Inputs explained

FieldWhat to enterQT intervalIn msHeart rateIn bpm

### What each result means

- **RR interval** = 60÷[Heart rate]
- **QTc (Bazett)** = [QT interval] ÷ sqrt([RR interval])
- **QTc (Fridericia)** = [QT interval] ÷ cbrt([RR interval])
- **QTc (Framingham)** = [QT interval] + 154×(1 - [RR interval])

### Example values

How the main result changes when **QT interval** changes and everything else stays at the example values above:

QT interval (ms)QTc (Bazett) (ms)200224300335400447500559600671800894
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — QT interval: 400 ms; Heart rate: 75 bpm.

Results — RR interval = 0.8 s; **QTc (Bazett) = 447 ms**; QTc (Fridericia) = 431 ms; QTc (Framingham) = 431 ms.

## FAQ

**Which formula should I use?**
Bazett is the most common but overcorrects at high heart rates; Fridericia is preferred above about 90 bpm.

**Why does QTc matter?**
Prolonged QTc increases the risk of dangerous arrhythmias.

**What formula does the QTc Calculator use?**
RR = 60 ÷ HR (s).


## Sources

- [Rautaharju PM et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the ECG, Part IV. Circulation, 2009](https://pubmed.ncbi.nlm.nih.gov/19228822/)