What reading ease and grade level measure
The Flesch Reading Ease score rates text from 0 to 100 based on two things: how many words are packed into the average sentence, and how many syllables are packed into the average word. Higher scores mean easier text, a score in the 60s to 70s is considered plain English, while anything below 30 reads like an academic paper. The Flesch-Kincaid Grade Level uses the same two inputs to estimate the U.S. school grade a reader would need to follow the text comfortably. Both formulas care only about sentence length and syllable count, not vocabulary difficulty, tone, or whether the ideas actually make sense.
How to improve a score
Shorter sentences do more for your score than almost anything else, since sentence length is weighted heavily in both formulas. Breaking a 30-word sentence into two or three shorter ones, trading semicolons for periods, and cutting throat-clearing phrases all bring the average down fast. On the word side, swap multi-syllable words for shorter synonyms where you can: "use" instead of "utilize," "help" instead of "facilitate." Reading your draft out loud is a quick way to catch sentences that have grown too long to say in one breath.
Where these formulas fall short
Flesch scores were built in the 1940s for English prose and count syllables with a simple heuristic, so they miss a lot. A short sentence packed with jargon can score as "easy" even though no one outside the field would understand it. Technical terms, acronyms, and proper nouns get treated the same as common words, and passive voice or muddled logic won't hurt your score at all even though they hurt real readability. Treat the number as a rough proxy for sentence and word length, not a certification that your writing is clear.