This study examined the concurrent validity of a tummy time questionnaire and time-use diary against an accelerometer measure. Participants were 29 parents and their 6-month-old infants from the Early Movers project in Edmonton, Canada. Tummy time was concurrently measured using a parental questionnaire, a time-use diary, and a validated GENEActiv accelerometer. In participants with data on all measures (n = 26), relative (Spearman's rank correlations) and absolute (Wilcoxon signed-rank tests and Bland-Altman plots) concurrent validity were examined. The questionnaire (r[subscript s] = 0.60) and time-use diary (r[subscript s] = 0.80) tummy time measures were significantly correlated with the accelerometer measure, with large effect sizes (r > 0.50). Compared to the accelerometer measure of tummy time, a significant difference in mean rank was observed for the questionnaire measure but not for the time-use diary measure. Bland--Altman plots showed a significant mean difference in tummy time between the accelerometer and questionnaire measures (42 min/d; 95% limits of agreement: -73,157 min/d) but not between the accelerometer and time-use diary measures (2 min/d; 95% limits of agreement: -47,51 min/d). These preliminary findings indicate both subjective measures may be appropriate for infant studies examining associations with tummy time and/or comparing tummy time between samples. The time-use diary may also provide a relatively precise estimate of tummy time in prevalence studies.