Background: According to the US Institute of Medicine guideline, preschool-aged children should participate in ≥15 minutes of physical activity (PA) per hour or 3 hours per day over 12 hours. Examinations of PA guideline compliance to date averaged time spent in PA over several days; however, children could exceed the guideline on some days and not on others. Therefore, this cross-sectional study examined PA guideline compliance in preschool children based on number of minutes per hour (average method) and percentage of days the guideline was met (everyday method). Methods: PA was measured by accelerometry during the preschool day for up to 10 days in 177 children (59.3% males, M age = 4.23). Minutes per hour and percentage of time in light, moderate to vigorous, and total PAs were calculated. Percentage of days in compliance was determined by number of days in compliance (defined as the child active on average ≥15 min/h) divided by total accelerometer days. Results: Children engaged in PA, on average, 17.01 minutes per hour, suggesting that on average, children are meeting the guideline. However, children were only in compliance with the PA guideline 62.41% of assessment days. Conclusions: Findings demonstrate the importance of examining compliance with both the average and everyday methods to more accurately portray level of Institute of Medicine PA guideline compliance.