# Gunning Fog Index Calculator

> The Gunning Fog index estimates the years of formal education a reader needs to understand a piece of text on a first reading. Unlike the Flesch formulas it counts complex words - words of three or more syllables - rather than syllables overall, which makes it stricter on jargon-heavy business and technical writing.

Source: https://rankcert.com/tools/gunning-fog-index-calculator
Free, no signup. Updated: 2026-09-08

## How to use it

1. Paste your text - a full article gives a far steadier result than a paragraph.
2. Read the Fog index alongside the count and percentage of complex words driving it.
3. Cut the complex-word share first; it is the input Fog weights most heavily.

## Gunning Fog scores in context

The formula is 0.4 x (words per sentence + 100 x complex word share), where a complex word has three or more syllables. Robert Gunning devised it in 1952 for newspaper editors.

| Fog index | Means | Comparable to |
| --- | --- | --- |
| 6 | Sixth grade | Easy-reading tabloid press |
| 8 | Eighth grade | Popular novels, good web copy |
| 10-12 | High school | Broadsheet newspapers |
| 13-16 | University | Trade journals, technical manuals |
| 17+ | Postgraduate | Academic and legal writing |

## Questions

### What is a good Gunning Fog score?

Aim for 8 to 10 for a wide audience and under 12 for anything meant to be read quickly. Above 17 you are writing for people who are being paid to read it.

### How is the Gunning Fog index calculated?

Add average words per sentence to the percentage of complex words, then multiply by 0.4. A complex word is three or more syllables, excluding proper nouns, familiar compound words and verb forms made three syllables only by an -ed or -es ending.

### What counts as a complex word?

Three syllables or more. Gunning's original rules excluded proper nouns, easy compounds like bookkeeper, and words that only reach three syllables through an inflected ending. Automated tools including this one apply the syllable rule directly, so expect a slightly stricter score than a hand count.

### How is Gunning Fog different from Flesch-Kincaid?

Flesch-Kincaid averages syllables across every word, so many short words dilute a few long ones. Fog counts what share of words are long, so jargon shows up more sharply. For business and technical writing Fog is usually the more revealing of the two.

### Why is my Fog score higher than my Flesch-Kincaid grade?

Because your text has a concentration of long words rather than a uniform spread. That gap between the two scores is itself the signal: it means jargon, not sentence structure, is what is making the page hard.

### Does the Fog index penalise technical terms unfairly?

It penalises them accurately - a three-syllable term is harder for a newcomer regardless of how routine it feels to you. Whether that matters depends on your reader. For internal engineering docs, ignore it; for a landing page, do not.

### Who invented the Gunning Fog index?

Robert Gunning, a US businessman who founded a consultancy in 1944 to fix what he called 'foggy writing' in newspapers and business documents. He published the index in 1952.

### How much text do I need?

At least 100 words, and ideally several hundred. The complex-word percentage is unstable on short samples - one technical term in a 20-word snippet swings the score by several grades.

## Related tools

- [Word Counter](https://rankcert.com/tools/word-counter): Count words, characters, sentences and paragraphs, with reading time, speaking time and a Flesch readability score. Everything runs in your browser.
- [Reading Time Calculator](https://rankcert.com/tools/reading-time): Estimate how long your article takes to read and to speak aloud, so you can put an honest number at the top of the page.
- [Keyword Density Checker](https://rankcert.com/tools/keyword-density): See which words your content actually repeats and at what percentage, with stop words excluded, so you can spot keyword stuffing before publishing.
- [Readability Checker](https://rankcert.com/tools/readability-checker): Score your writing on Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, SMOG and Coleman-Liau at once, and see which one your text fails.
- [Flesch Reading Ease Calculator](https://rankcert.com/tools/flesch-reading-ease-calculator): Score any text on the Flesch Reading Ease scale from 0 to 100, see the audience it reads for, and get the sentence length and syllable numbers behind the score.
- [Flesch-Kincaid Grade Level Calculator](https://rankcert.com/tools/flesch-kincaid-grade-level-calculator): Get the US school grade level any text is written for, using the Flesch-Kincaid formula, plus the sentence length and syllable numbers behind the result.