Using data from the 1979 National Longitudinal Survey of Youth, we describe the correspondence between intended family size and observed fertility for US men and women in the 1957–64 birth cohorts. Mean fertility intentions calculated from reports given in the mid-20s modestly overstate completed fertility. But discrepancies between stated intent and actual fertility are common—the stated intent at age 24 (for both women and men) is more likely to miss than to match completed fertility. We focus on factors that predict which women and men will have fewer or more children than intended. Consistent with life-course arguments, those unmarried, childless, or (for women) still in school at approximately age 24 were most likely to underachieve their intended parity (i.e., had fewer children than intended at age 24). We discuss how such discrepancies between intentions and behavior may cumulate to produce sizable cross-group fertility differences.