With 86% of the words, you might understand only 38% of an anime's lines

Coverage tells you the percentage of spoken words you know, not how many lines you can follow. Measured in Frieren and seven other anime.

Say you want to watch Frieren, so you learn the 500 most common words in the show. A coverage calculator says that you now know 85.9% of the words spoken.

By the third pause to look up a word, your tea has gone cold. With those 500 words, you know every word in 1,151 of the first 3,000 lines. That's 38.4% of them. The other 1,849 lines each contain at least one word you don't know.

Coverage is the number most learning sites quote. It's the percentage of spoken words that you know, so a particle spoken a thousand times counts a thousand times. The words at the very top of the Frieren list are all grammar pieces like の (of, 's) and は (topic marker), so the top 100 words alone give you 68.3% coverage. You'd follow only 8.5% of the lines.