ASQ age calculator

Enter the date of birth, the questionnaire date and how early the baby was born. You get the age to use for scoring, whether to adjust for prematurity, and the ASQ-3 and ASQ:SE-2 interval from the age chart.

By the Calcist team · Checked against known answers · Updated October 29, 2026

Private: calculated on your device. Nothing you type is sent anywhere.

A general estimate from a published formula, not medical advice.

Next: Need an exact age for something else? Use the age calculator or count days with the days between dates calculator.

The ASQ rule for prematurity

The Ages & Stages Questionnaires (ASQ-3 and ASQ:SE-2) are filled in by parents to screen a young child's development. A baby born early is compared with children of the same developmental age, so the ASQ developers say to adjust the age when:

the child was born 3 or more weeks before the due date (at or before 36 weeks), and
the child is under 2 years old chronologically. From age 2, use the actual age.

The same guidelines apply to the ASQ-3 and the ASQ:SE-2. ASQ's developers used 39 weeks as a full-term pregnancy, so weeks premature = 39 weeks − gestational age at birth. (They note programs using 38 or 40 weeks may do so as long as they're consistent; this calculator uses 39.)

Adjusted age = chronological age − weeks premature

Worked example (from the ASQ developers)

A child born March 10, 2017 is screened on July 15, 2018 and was born 5 weeks (35 days) early.

Chronological age: 2018-07-15 minus 2017-03-10 = 1 year, 4 months, 5 days.
The child is under 2 and was 3 or more weeks early, so adjust.
35 days can't come out of 5 days, so borrow a month as 30 days: 1 year, 3 months, 35 days.
Subtract 35 days: adjusted age = 1 year, 3 months, 0 days (15 months). On the age chart that's the 16 month ASQ-3 and the 18 month ASQ:SE-2.

ASQ-3 age ranges

Child's age	ASQ-3 questionnaire
1 mo 0 d – 2 mo 30 d	2 month
3 mo 0 d – 4 mo 30 d	4 month
5 mo 0 d – 6 mo 30 d	6 month
7 mo 0 d – 8 mo 30 d	8 month
9 mo 0 d – 9 mo 30 d	9 or 10 month
10 mo 0 d – 10 mo 30 d	10 month
11 mo 0 d – 12 mo 30 d	12 month
13 mo 0 d – 22 mo 30 d	14, 16, 18, 20 or 22 month (each covers the month before and its own month)
23 mo 0 d – 25 mo 15 d	24 month
25 mo 16 d – 28 mo 15 d	27 month
28 mo 16 d – 31 mo 15 d	30 month
31 mo 16 d – 34 mo 15 d	33 month
34 mo 16 d – 38 mo 30 d	36 month
39 mo 0 d – 44 mo 30 d	42 month
45 mo 0 d – 50 mo 30 d	48 month
51 mo 0 d – 56 mo 30 d	54 month
57 mo 0 d – 66 mo 0 d	60 month
66 mo 1 d – 77 mo 30 d	72 month

From the ASQ-3 and ASQ:SE-2 combined age administration chart. Always check the age range printed on the questionnaire itself.

How the dates are counted

Chronological age is counted in calendar years, months and days, borrowing the days of the previous month when needed, like the age calculator. When subtracting prematurity, a month is borrowed as 30 days, as in the ASQ worked example. Results can differ by a day from other tools near month ends; the publisher's own ASQ Age Calculator is the reference if a child is right at the edge of an interval.

Limitations

This only works out ages and intervals. It doesn't score questionnaires or interpret results; that's for the program or professional using ASQ.
If the due date was set by an early ultrasound, weeks premature can be worked out from the due date instead; enter whichever your program uses.
ASQ is a screening tool, not a diagnosis. Questions about a child's development belong with their pediatrician.

Sources

How we checked this

Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:

ASQ example: born 2017-03-10, screened 2018-07-15, 5 weeks early → 1 year, 3 months, 0 days ✓
…which is the 16 month ASQ-3 ✓
Born at 31 weeks (8 weeks early), 7 months 16 days old → adjusted 5 months, 20 days, 6 month ASQ-3 ✓
Born 2 weeks early: no adjustment ✓
Edge case: 2 years or older uses actual age (2 years, 2 months → 27 month ASQ-3) ✓

Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.

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Questions people ask

When do you adjust age for prematurity on the ASQ?

When the child was born 3 or more weeks early and is under 2 years old chronologically. From age 2, use the actual age.

How do you calculate adjusted age for ASQ?

Subtract the weeks of prematurity from the child's chronological age on the day the questionnaire is completed. Weeks premature = 39 weeks − gestational age at birth.

Does ASQ:SE-2 use adjusted age?

Yes. The ASQ developers say the guidelines are the same as for ASQ-3: adjust if born 3 or more weeks early and under 2.

What counts as full term for ASQ?

The ASQ developers used 39 weeks as a full-term pregnancy in their research.

Which questionnaire do I use for a 15-month-old?

On the ASQ-3 chart, 15 months 0 days to 16 months 30 days uses the 16 month questionnaire; on ASQ:SE-2, 15 months 0 days to 20 months 30 days uses the 18 month questionnaire.

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