As a partial replication of Laufer and Cobb (2020), the study determines the proportion of graded reader texts covered by basewords, inflected words, and derived words. Over 100 graded readers from various publishers and across various levels were manually analyzed to determine the number of proper nouns, marginal words, basewords, inflectional forms, and derivational forms of each. Through this analysis, I developed a list of the most frequent affixes in the graded reader corpus and assessed the contribution of affixed words to lexical thresholds of 95%, 98%, and 99%. The results show that when basewords, inflectional forms, and proper nouns are assumed to be known, relatively few derivational affixes are usually enough to reach 98% coverage due to the nature of graded texts versus other text types. This has pedagogical implications for practitioners who advocate graded readers for reading fluency development, requiring a high degree of coverage (i.e. 99% or 100%).