Gunning Fog Index Calculator
Score your text live with six classic readability formulas: Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau and ARI.
Processed entirely in your browser — nothing you enter here is ever uploaded.
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About this tool
This page opens the readability checker with the Gunning Fog card highlighted — paste your text and the fog index updates live with each change.
The Gunning Fog index estimates the years of formal education a reader needs: 0.4 × (average sentence length + 100 × complex words ÷ words), where complex words have three or more syllables. Business writing usually targets a fog index below 12.
This tool counts complex words with a syllable heuristic and skips the manual proper-noun exceptions of the original method, and the formula itself is English-calibrated — use the score as a comparative signal. Five more formulas are computed alongside it, all locally in your browser.
Example. The cat sat on the mat. is counted as 6 words and 1 sentence, and Flesch Reading Ease is clamped to 100 because the raw score sits above the scale.
Limit. Syllables are vowel groups plus a silent-e rule, so the six English formulas are not recalibrated for other languages.