TL;DR: a readability score is a formula, not an opinion — most (including Flesch Reading Ease) reduce to sentence length and syllable count, which means the same two levers explain almost every low score. Knowing the formula tells you exactly what to fix instead of vaguely "simplifying". Pair this guide with Word Frequency Counter, Text Difference, Remove Extra Spaces and Character Counter.
Readability formulas estimate how hard text is to read using measurable properties of the text itself — not meaning, just structure.
What the formula actually measures
The Flesch Reading Ease formula is 206.835 − 1.015 × (words/sentences) − 84.6 × (syllables/words) — a higher score means easier reading, and the two inputs are just average sentence length and average syllables per word. It has no concept of whether the content is logically clear, whether jargon is defined, or whether the argument makes sense — a text can score "easy" while being confusing, and score "difficult" while being perfectly clear to its intended audience.
Why long sentences hurt more than long words
Sentence length carries a heavier weight in the formula (1.015) than word length does relative to typical variation, and in practice it's usually the bigger lever: a 40-word sentence with three clauses taxes working memory regardless of how simple its individual words are, because the reader has to hold the whole structure before the meaning resolves. Splitting one long sentence into two shorter ones often moves the score more than swapping several words for shorter synonyms.
Syllable counting is an estimate, not a dictionary lookup
Most implementations count syllables algorithmically (counting vowel groups, with exceptions for silent trailing "e" and similar rules) rather than looking up each word in a pronunciation dictionary, which means the count is an approximation — usually close enough for the aggregate score across a whole document, but not something to trust word-by-word for a single tricky term.
What actually moves the score
- Split compound sentences joined by "and", "which", or a semicolon into two separate sentences where the meaning allows it.
- Replace a multi-syllable word with a shorter synonym only when the shorter word means the same thing — accuracy first, score second.
- Remove or move parenthetical asides that force the reader to hold extra context mid-sentence.
- Recheck after each pass — the biggest single-sentence fix usually helps more than uniformly trimming several words across the whole text.
Common mistakes to avoid
- Chasing a specific target score by mechanically swapping words, which can make writing sound artificially simplistic.
- Assuming a high readability score means the content is actually clear — the formula can't measure logic or jargon.
- Ignoring that the audience matters: technical documentation for specialists doesn't need the same score as public-facing copy.
- Treating one very long, complex sentence and ten slightly-long ones as equally worth fixing — the single worst sentence usually moves the score the most.
A readability score tells you where to look, specifically sentence length and word length — it doesn't replace judgment about whether the simplified version still says what you meant.