QTc Calculator: QT interval

QTc Calculator computes the corrected QT interval with five formulas and shows how the value compares with normal ranges for men, women and children. How to use Choose male, female or child, enter heart rate or the RR interval, and the QT duration in milliseconds. The result appears straight away. If the QRS is wide (120 ms or more), enter it too and the app will apply a correction. What it calculates • QTc by Bazett, Fridericia, Framingham, Hodges and Rautaharju — all five formulas on one screen. • Choose the main formula in Settings, or keep the automatic choice: Bazett at 60–90 bpm, otherwise Fridericia. • The formula list marks the one that is most accurate at the entered heart rate. • Grading by the AHA/ACCF/HRS 2009 thresholds: normal, borderline, prolonged, markedly prolonged (500 ms or more) and short QT. • A colour scale shows where the result sits against the thresholds. Wide QRS With bundle branch block the usual QTc is overestimated. The app shows two published corrections: • Bogossian (2014): 48.5% of the QRS duration is subtracted from QT, then the rate correction is applied. The calculation is shown step by step. • Rautaharju (2004): a separate formula for bundle branch block that takes heart rate, QRS width and sex into account. Reference • QTc normal values for men, women and children aged 1–15. • Danger values and signs of short QT. • Which formula to use and how to measure QT on an ECG. • All formulas with units explained. Handy • A one-line summary to copy or share. • Light and dark theme. • Works offline; data stays on your phone. Important The formulas and thresholds come from studies of patient groups. The result is a guide for reading the ECG, not a diagnosis, and depends on how accurately QT and RR are measured. The app is not a medical device. The ECG is assessed by a doctor.

Version 2.0 — a complete redesign. • New look with light and dark themes. • All 5 QTc formulas on one screen, graded against normal ranges. • Choose the main formula in Settings or let the app pick by heart rate. • Wide QRS correction: Bogossian and Rautaharju, shown step by step. • Reference: normal values, danger values, how to measure QT. • Copy or share a one-line summary.