0–6 years Evidence-based Free & private

Baby Age Calculator — Months, Weeks & Days

Convert your baby's date of birth to exact age in years, months, weeks, and days. Perfect for milestones, vaccinations, and pediatric visits.

Start calculating Learn about Baby Age Calculator — Months, Weeks & Days
Baby seated on clouds beneath a soft pastel arch of month markers
Category
Development
Trust
Medical-grade
Enter your child's date of birth to see their precise age.
Medically reviewed by ASQCalculator Editorial Team
Last reviewed: June 25, 2026Review policyMethodology

Understanding this tool

Plain-language explanations grounded in current pediatric evidence.

TL;DR

Enter your baby's date of birth (and an optional 'as of' date) to get exact age in years, months, weeks, and days. Pediatric milestones, vaccines, and screening tools all reference age in completed months under 24 months.

What it is

The Baby Age Calculator converts a date of birth into your child's exact age in years, months, weeks, and days. Pediatric milestones, growth charts, vaccinations, and developmental screening tools (like ASQ-3) all reference age in months.

How it's calculated

We compute the calendar difference between two dates, accounting for variable month lengths. Total months, weeks, and days are derived from the elapsed time between dates.

When to use it

Use this any time you need to give a precise age for a pediatric appointment, vaccination, growth tracking, or developmental screening questionnaire.

Who should use it

Parents, caregivers, nannies, pediatricians, nurses, early-childhood educators, and therapists.

Clinical importance

Most pediatric tools use age in months under 24 months and decimal years thereafter. Reporting age accurately ensures growth percentiles and screening cutoffs are interpreted correctly.

Example

A child born on 12 Jan 2024 is, on 12 Jun 2026, exactly 2 years, 5 months, 0 days (29 months, ~126 weeks).

How to use this calculator

  1. 1
    Enter date of birth
    Pick your baby's birth date in the first field.
  2. 2
    Choose the reference date
    Defaults to today. Change it to plan future milestones or vaccinations.
  3. 3
    Read the breakdown
    See age in years/months/days plus totals in months, weeks, and days.
  4. 4
    Use for a screener
    For preterm babies under 24 months, convert with the Corrected Age calculator before using growth or screening tools.

Common mistakes to avoid

  • Reporting age in years for a baby under 2 — pediatric tools expect months.
  • Using chronological age for a preterm baby on growth charts under 24 months.
  • Rounding months down when a screener needs the exact month interval.

Glossary

Chronological age
Time elapsed since birth, regardless of gestational age at birth.
Completed months
Number of whole months reached — a child who is 11m 27d is still '11 months'.
Decimal age
Age expressed as a fractional year, e.g. 2.4 years; common in school-age tools.

Medical references

Frequently asked questions

Answers parents and pediatric professionals ask most often about this tool.

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    Aligned with AAP & CDC
  • Evidence-based
    Official ASQ-3 cutoffs
  • Mobile-first
    Built for phones & tablets
Medical disclaimer. This calculator is an educational tool and does not replace evaluation by a qualified pediatric clinician. If you are concerned about your child's development or health, contact your pediatrician.