Gunning Fog Index calculator
Calculate the Gunning Fog Index of any text. Paste text below; your Gunning Fog Index score is highlighted alongside the other formulas.
Your scores will appear here. Paste some text above, or use the sample. Everything is calculated in your browser.
The Gunning Fog Index formula
Fog = 0.4 × [ (words ÷ sentences) + 100 × (complex words ÷ words) ]
It combines:
- Average sentence length in words
- Percentage of “complex” words: three or more syllables, not counting proper nouns, familiar compound words, or words that only reach three syllables through endings like -es, -ed or -ing
Where it came from
Robert Gunning, an American businessman who had worked in newspaper and textbook publishing, introduced the index in 1952 in his book The Technique of Clear Writing. He found that much business and news writing was full of “fog”: needless complexity.
When to use it
Business writing, reports and journalism. Gunning suggested that text for a wide audience should score below 12, and that popular publications sit around 8–10.
Watch out for
Not every long word is hard: “interesting” and “family” count as complex, while short but rare words like “ergo” do not. Treat the score as a signal to check word choice, not a verdict.
Reading the grade
| Score | Reader |
|---|---|
| 1–5 | Primary school, age 6–11 |
| 6–8 | Middle school, age 11–14: general public |
| 9–12 | High school, age 14–18 |
| 13–16 | College |
| 17+ | Graduate / professional |
Other formulas
Flesch Reading Ease & Flesch-Kincaid · SMOG Index · Coleman–Liau Index · Automated Readability Index
Questions people ask
What is a good Gunning Fog score?
Aim for 8–10 for general audiences, and keep it under 12 for anything meant to be widely read. Scores of 17 and above are typical of academic writing.
What counts as a complex word in the Fog Index?
Words of three or more syllables, excluding proper nouns, familiar jargon, compound words made of short words, and words that only reach three syllables because of -es, -ed or -ing endings.
How is Gunning Fog different from Flesch-Kincaid?
Flesch-Kincaid uses average syllables per word across all words. Gunning Fog only looks at the share of long (3+ syllable) words, so a text full of two-syllable words can score lower on Fog than on Flesch-Kincaid.