Gunning Fog Index
A grade-level score tuned for business writing. Penalizes multi-syllable jargon.
The Gunning Fog Index was developed by Robert Gunning in 1952 for business communication. The formula: 0.4 × [(words/sentences) + 100 × (complex words/words)]. "Complex words" are those with 3+ syllables, excluding proper nouns, compound words, and common suffixes (-ed, -es, -ing). This makes Fog more sensitive to jargon than Flesch-Kincaid. A Fog Index of 8 is ideal for mass media; 12 is the upper limit for comfortable reading. Government and legal documents often score above 18.