What is my Gunning fog index?
Paste a passage of about 100 words or more, or type its counts by hand. The fog calculator works out the Gunning fog index, an estimate of the years of formal education a reader needs to understand the text on a first reading.
- Fog index
- 10.4
The passage has a Gunning fog index of 10.4: 45 words in 3 sentences.
Plain: fine for a wide audience
- Easy: near-universal
- Plain: fine for a wide audience
- Hard for a wide audience
- Words per sentence
- 15
- Complex words
- 11.11
- Words
- 45
- Sentences
- 3
- Complex words counted
- 5
- Complex words found
- estimates, complicated, terminology, sometimes, university
Fog index: 10.4. The passage has a Gunning fog index of 10.4: 45 words in 3 sentences.
How to calculate
A fog calculator for the Gunning fog index: paste a text, or type its word, sentence and complex word counts, to estimate the years of schooling a reader needs.
Example with the default inputs (I have Text, Your text The fog index estimates the years of schooling a reader needs to follow a text on the first reading. Short sentences and plain words keep the number low. Long sentences full of complicated terminology push it higher, sometimes beyond the level of a university graduate.): The passage has a Gunning fog index of 10.4: 45 words in 3 sentences.
Method: Fog index = 0.4 × (words ÷ sentences + 100 × complex words ÷ words); a complex word has 3 or more syllables.
- From text, syllables are counted by vowel groups, which is close to, but not the same as, counting them by ear.
- Hyphenated words, names (a capital letter not at the start of a sentence) and syllables added by -es, -ed or -ing do not make a word complex.
- The index assumes whole sentences of ordinary prose; lists, code and headings skew it.
Worked examples
Each example is checked against the calculator on every build.
- I have Counts, Words 100, Sentences 5, Complex words 10 gives Fog index 12, Words per sentence 20, Complex words 10.Source: Gunning fog index, Wikipedia (0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]; complex words have three or more syllables, not counting proper nouns, familiar jargon, compound words, or the common suffixes -es, -ed and -ing; Robert Gunning, The Technique of Clear Writing, McGraw-Hill, 1952), https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03)
- I have Counts, Words 230, Sentences 14, Complex words 21 gives Fog index 10.223602, Words per sentence 16.428571, Complex words 9.130435.Source: Gunning fog index, Wikipedia (0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]; complex words have three or more syllables, not counting proper nouns, familiar jargon, compound words, or the common suffixes -es, -ed and -ing; Robert Gunning, The Technique of Clear Writing, McGraw-Hill, 1952), https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03)
- I have Text, Your text Communication is important. Anna and Michael understand everything. We tested the well-organized interface. gives Words 13, Sentences 3, Complex words counted 5, Complex words found communication, important, understand, everything, interface.Source: Gunning fog index, Wikipedia (0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]; complex words have three or more syllables, not counting proper nouns, familiar jargon, compound words, or the common suffixes -es, -ed and -ing; Robert Gunning, The Technique of Clear Writing, McGraw-Hill, 1952), https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03)
How it works
Fog index = 0.4 × (words ÷ sentences + 100 × complex words ÷ words).
The index shows with 1 decimal, words per sentence and percent complex words with 2, each rounded half up from the exact value. The bands: below 8 easy; 8 up to 12 plain; 12 or more hard for a wide audience.
Counting a pasted text
- Words: each run of letters or digits, where an apostrophe (' or ’) or a hyphen (- or ‐) between two letters or digits keeps the run together (
[\p{L}\p{N}]+(['’‐-][\p{L}\p{N}]+)*). - Sentences: split the text at each run of
.,!or?; each piece that holds at least one word is a sentence. Only words in these pieces are counted. - Syllables of a word: keep the letters a to z of the lower-cased word; count the groups of consecutive vowels (a, e, i, o, u, y); if there is more than one group and the word ends in "e" but not "le", take one off; at least 1.
- Complex word: a word is complex when the syllables of its stem are 3 or more, where the stem is the word with one final "es", "ed" or "ing" removed. A word is never complex when it holds a hyphen, or when it starts with a capital letter and is not the first word of its sentence (a name).
- The complex words found are listed once each, lower-cased, in the order found (up to 30).
Counts typed by hand
Words 1 to 10⁹, sentences 1 to 10⁹, complex words 0 to 10⁹. More complex words than words gives no answer. A text with no words gives no answer.
Worked examples by hand
100 words, 5 sentences, 10 complex. 100 ÷ 5 = 20; 100 × 10 ÷ 100 = 10; 0.4 × 30 = 12.0.
230 words, 14 sentences, 21 complex. 230 ÷ 14 = 16.43; 2,100 ÷ 230 = 9.13; 0.4 × 25.56 = 10.22, shown 10.2.
“Communication is important. Anna and Michael understand everything. We tested the well-organized interface.” 3 sentences of 3, 5 and 5 words: 13 words. Syllables: communication (o, u, i, a, io) 5; important 3; understand 3; everything (e, e, y, i) 4; interface 4, less the final e, 3: 5 complex words. Anna is the first word of its sentence but has 2 syllables; Michael is a name; tested has the stem "test"; well-organized is hyphenated. Fog = 0.4 × (13 ÷ 3 + 500 ÷ 13) = 0.4 × 42.79 = 17.1.
Other questions people ask
What is the Gunning fog index?
A readability score that Robert Gunning published in 1952 in The Technique of Clear Writing. It estimates the years of formal education a reader needs to understand a text on the first reading: 12 is about the level of a US high school senior.
How is the fog index calculated?
Take the average number of words per sentence, add the percentage of complex words (three syllables or more), and multiply by 0.4. 100 words in 5 sentences with 10 complex words gives 0.4 × (20 + 10) = 12.
What is a good fog index?
Text for a wide audience usually needs a fog index below 12, and text that nearly everyone must understand below 8. Most popular magazines and newspapers aim between 8 and 12.
Which words count as complex?
Words of three or more syllables, except names, hyphenated compound words, and words that reach three syllables only through the ending -es, -ed or -ing (“created” counts like “create”). Gunning also left out familiar jargon, which a program cannot judge.
Why does my score differ from another fog calculator?
Programs count syllables and sentences in different ways. This one counts vowel groups, so a word like “area” counts as two syllables, not three. Use the counts mode to type your own counts.
How do I lower my fog index?
Split long sentences and use short, common words. Both parts of the formula count the same, so cutting the average sentence from 25 to 15 words lowers the index by 4.