Most readability tools give you one score. This one runs all six standard algorithms at once (Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau, and ARI) and averages them, so you are not guessing which formula your publisher or editor uses.
What each algorithm tells you
Six different formulas, six slightly different answers. Each one targets a different audience or use case, and they disagree on purpose. Looking at all of them together is more honest than picking one.
Flesch Reading Ease
Rudolf Flesch built this in 1948, and it remains the one score where higher means easier. 60 is the rough cutoff for general audiences; below 30 is academic territory. Everything else outputs a grade level. This one does not.
Flesch-Kincaid Grade Level
The same inputs as Flesch Reading Ease, recast as a US school grade. Commissioned by the US Navy in 1975 to grade technical manuals. Microsoft Word's built-in score uses this. Most widely cited in publishing.
Gunning Fog Index
Robert Gunning built this in 1952. Fog penalises long words harder than Flesch-Kincaid does: a single polysyllabic jargon word drags your Fog score more than it moves your Flesch grade. The output is years of formal education needed to read fluently. Standard prose lands around 8.
SMOG Index
"Simple Measure of Gobbledygook" by G. Harry McLaughlin (1969). Designed for healthcare and government materials where comprehension is critical. Most accurate on samples of 30+ sentences. Now the standard in medical writing.
Coleman-Liau Index
Built by Coleman and Liau (1975) for digital text. Uses character counts instead of syllables, which avoids the error introduced by syllable-counting heuristics. Often more consistent than Flesch-Kincaid on machine-generated or unusual text.
Automated Readability Index (ARI)
Also character-based. Developed by Smith and Senter (1967) for the US Air Force to grade printed materials. Standard in US government documents.
How to use the scores
Don't optimize for a single score. Write naturally first, then check. If multiple scores cluster around grade 12+ but your audience is general readers, the prose is too dense. Common fixes that lower readability score (make it easier):
- Shorter sentences (avg 14–18 words is the sweet spot for general prose)
- More common words (replace polysyllabic Latinate words with shorter Anglo-Saxon equivalents where possible)
- Active voice (cuts word count and syllables both)
- Break long paragraphs (paragraphs don't affect the math directly, but shorter ones encourage shorter sentences)
Conversely, if you're writing literary fiction or technical prose for an expert audience, a "high" score (grade 12+) may be exactly right.
Reading levels by content type
| Content | Typical Flesch-Kincaid grade | Reading age |
|---|---|---|
| Children's picture books | 1–3 | 6–8 |
| Middle grade fiction | 4–6 | 9–11 |
| YA novels | 5–7 | 10–12 |
| News articles (general press) | 6–9 | 11–14 |
| Adult commercial fiction | 5–9 | 10–14 |
| General-audience blog posts | 7–9 | 12–14 |
| Business / trade publications | 10–12 | 15–17 |
| Adult literary fiction | 8–14 (varies wildly) | 13–19 |
| Academic / scientific papers | 14–18 | 19–23 |
Beyond a single check
Readability is one snapshot. The harder question is whether your writing matches your audience consistently across a full manuscript or a year of posts. That takes longer data than a single paste. Authorlytica logs your daily word count and session history. Paste this week's draft chapter here to check its score, then log the session in Authorlytica so you can see whether the prose is getting cleaner as your pace picks up.