Note: Different formulas are used for German and English to calculate readability. If the system language is German, the formula adapted by Toni Amstad for German texts is used, otherwise the formula for English texts is used. Further information on the Flesh-Kinkaid formula can be found on Wikipedia:
[English Wikipedia article](https://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readability_tests)
[German Wikipedia article](https://de.wikipedia.org/wiki/Lesbarkeitsindex)
The number of sentences, words and syllables are required to calculate the Flesh-Kinkaid formula. The following explains how these elements are determined in this program. This can help to better understand the calculation result.
An algorithm is used to determine the number of syllables, which generally provides good accuracy. However, due to the complexity of the language, there are a few special cases that are not taken into account. Also foreign words can lead to distorted values. In general, the longer a text is, the more accurate the syllable count will be.
Due to different calculation methods, other tools that calculate the readability index may produce different results.