Countermovement jump (CMJ) force data are often time-normalized so researchers and practitioners can study the effect that sex, training status, and training intervention have on CMJ strategy, the so-called force-time curve shape. Data are often collected on an individual basis and then averaged across groups of interest. However, little is known about the within-subject agreement of the CMJ force-time curve shape, and this formed the aim of this study. Fifteen men performed 10 CMJs on in-ground force plates, force-time curves were plotted, and their shape categorized as exhibiting either a single peak (unimodal) or a double peak (bimodal). Percentage agreement and the kappa coefficient were used to assess within-subject agreement. Over two and three trials 13% demonstrated a unimodal shape, 67% exhibited a bimodal shape, and 20% were inconsistent. When five trials were considered the unimodal shape was not demonstrated consistently, 67% demonstrated a bimodal shape, and 33% were inconsistent. Over 10 trials none demonstrated the unimodal shape, 60% demonstrated the bimodal shape, and 40% were inconsistent. The results of this study suggest that researchers and practitioners should ensure within-subject consistency before group averaging CMJ force-time data to help avoid errors that not doing so may cause.