Gunning Fog Index Calculator

What is Gunning Fog Index?

The Gunning Fog Index is the readability formula that treats long sentences and long words as equally expensive, which is what distinguishes it from the Flesch family. Its measure of difficulty is the percentage of complex words — three syllables or more — added to the average sentence length in words, scaled by 0.4 to land on the US grade system. Robert Gunning's own advice was to aim below 12 and never publish above 17; the index is popular in corporate and government plain-language work for exactly that concrete threshold.

How it works

The score is 0.4 times the sum of the average sentence length and the percentage of complex words, with complex words counted as anything of three syllables or more by the shared syllable heuristic. The classic method strips proper nouns and words made longer by -ed and -es before counting, which needs a dictionary and a part-of-speech tagger; this implementation counts every three-syllable word and states the consequence — the index reads slightly high, by around half a grade on ordinary prose. The two terms are reported separately so it is clear whether a high score is coming from the sentences or the vocabulary, which is the only way the number is actionable.

1. Enter your input. Type or paste your input into the field above — the tool responds instantly.
2. Review the result. Output updates live as you type. Everything runs entirely in your browser.
3. Copy or download. Use the Copy button to grab the result, or Download to save it as a file.

Examples

Realistic sample

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Common mistakes

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