Although previous studies have found a link between the child-directed speech learners receive and their vocabulary development, no previous studies have found a parallel link between early measures of overheard speech and vocabulary. This is despite the fact that children are able to learn words from overheard speech in laboratory settings (Shneidman & Woodward, 2015). Drawing on the idea that children preferentially attend to stimuli that are at a manageable level of complexity (Kidd, Piantadosi, & Aslin, 2012, 2014), the present research explores the possibility that children do not initially tune into overheard speech because it is too complex for their stage of lexical development. Using transcripts from CHILDES and the SBC, and estimates of vocabulary by age from the MB-CDI, we find that child-directed speech is significantly less complex than overheard speech through at least 30 months, suggesting children may only begin learning from more complex, overheard speech later.