# What is my Gunning fog index?

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.

- Page: https://www.acalculator.org/everyday-life/fog-calculator
- JSON spec: https://www.acalculator.org/everyday-life/fog-calculator.json
- Version: 77a2e14387ac

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| from | I have | A text to paste, or the counts of words, sentences and complex words. |
| t | Your text | Paste a passage of about 100 words or more, in whole sentences. |
| w | Words | The number of words in the passage. |
| s | Sentences | The number of sentences in the passage. |
| c | Complex words | Words of three or more syllables, as Gunning counts them. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| fog | Fog index | 0.4 × (words per sentence + percent complex words). |
| perSentence | Words per sentence | Words ÷ sentences. |
| percentComplex | Complex words | Complex words ÷ words × 100, in percent. |
| wordCount | Words | Words counted. |
| sentenceCount | Sentences | Sentences counted. |
| complexCount | Complex words counted | Words of 3 or more syllables. |
| complexList | Complex words found | The complex words in the text, in order, each once (up to 30). |

## Method

Fog index = 0.4 × (words ÷ sentences + 100 × complex words ÷ words); a complex word has 3 or more syllables.

## Assumptions

- 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

1. from = counts, w = 100, s = 5, c = 10 gives fog = 12, perSentence = 20, percentComplex = 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).
2. from = counts, w = 230, s = 14, c = 21 gives fog = 10.223602, perSentence = 16.428571, percentComplex = 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).
3. from = text, t = Communication is important. Anna and Michael understand everything. We tested the well-organized interface. gives wordCount = 13, sentenceCount = 3, complexCount = 5, complexList = 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).

## FAQ

### 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.

## Sources

- 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; developed by Robert Gunning in 1952, The Technique of Clear Writing, McGraw-Hill). https://en.wikipedia.org/wiki/Gunning_fog_index (retrieved 2026-10-03)