To determine the correct ASQ-3 interval for a child, you need to calculate a child's age in months and days. For easy age calculation, you can use our website calculator at or the free ASQ Calculator app available in the Apple and Google Play app stores. A by-hand method is described on page 65 of the ASQ-3 User's Guide. After determining a child's age, use the ASQ-3 Age Administration chart to select the correct interval (e.g., 6 month, 12 month). Each interval has an administration window; the window is approximately 2 months for the younger intervals and 6 months for the older intervals.