ASQ Age Calculator
The Ages & Stages Questionnaires, Third Edition (ASQ-3) has 21 questionnaires for 1 month to 66 months. Each has an age window. This page works out the child's age in months and days, applies the publisher's prematurity rule, and tells you which interval to use. It does not include or score any questionnaire items, and it isn't a screening result.
Before you start
Method : Age in months and days, publisher's prematurity rule, then the ASQ-3 age window.
Checked : Windows and prematurity rule read from Brookes publications on 2026-10-05; tests cover every chart edge we encode near 0, 24–27 and 66 months.
Review : not reviewed by Brookes Publishing or a developmental specialist. Not affiliated with ASQ or Brookes; no questionnaire content is reproduced.
Your entries stay in this browser tab; nothing is sent or stored.
How to Use This Calculator
- Enter the birth date and the date the questionnaire will be completed.
- Enter how many weeks before the due date the child was born (0 if on time).
- Press Find interval.
Methodology & assumptions
Edition: ASQ-3 (Third Edition) only; windows from the publisher's age administration chart (checked 2026-10-05).
Age: screening date minus birth date in months and days, borrowing 30 days for a month (as the chart's "30 days" bounds assume). Adjustment: if born ≥ 3 weeks early and under 24 months, subtract weeks × 7 days. Then find the window that contains the age. At 9 months 0–30 days either the 9- or 10-month questionnaire may be used.
Worked examples
On time: born January 10, 2026, screened July 9, 2026 → 5 months 29 days → 6 month questionnaire.
8 weeks early: same dates → 5 m 29 d − 56 days = 4 months 3 days → 4 month.
Window edge: 25 months 15 days → 24 month; 25 months 16 days → 27 month. Over 66 months 0 days is outside ASQ-3.
Understanding your result
If the child is within a week of a window's end, Brookes suggests waiting and using the next questionnaire. Only a trained professional should interpret ASQ scores.
Sources & further reading
- Brookes Publishing. ASQ-3 Age Administration Chart (excerpted from the ASQ-3 User's Guide, 2009).Questionnaire windows in months and days, 1 month 0 days to 66 months 0 days. Checked October 5, 2026.
- Brookes Publishing. Considerations when screening premature children (2018).Adjust only if 3 or more weeks premature and under age 2; subtract weeks premature from chronological age. Checked October 5, 2026.
- Brookes Publishing. FAQs about ASQ-4.ASQ-4 is in development with no publication date; this tool supports ASQ-3 only. Checked October 5, 2026.
Frequently Asked Questions
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