Baby Age Calculator
Calculate your baby's exact age in years, months, weeks, and days from their date of birth.
- Free to use
- Accurate results
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- Works on all devices
Your result
10 weeks
Age in weeks
AI explanation
Formula
Calendar-accurate years/months/days difference between birth date and as-of date; weeks = total days / 7Worked example
Born 2026-01-01, as of 2026-03-12
| Field | Value |
|---|---|
| Date of birth | 01-01-2026 |
| As of date | 12-03-2026 |
| Age in weeks | 10 |
| Total days | 70 |
Assumptions
- Uses calendar-accurate date arithmetic (not a flat 30-day month or 365-day year approximation).
- Informational only.
Frequently asked questions
Why is baby age often measured in weeks instead of months?
In the first few months, weekly milestones (feeding, sleep, growth checkpoints) change quickly, so pediatric guidance and growth charts often reference age in weeks for more precision during infancy.
When do people switch to measuring age in months?
Most parents and pediatric guidance shift to months around 3 months old, and to years after the first birthday, once developmental milestones are further apart.
Does this account for premature birth (corrected age)?
No — this shows chronological age from the actual birth date. For babies born prematurely, pediatricians often also track "corrected age" (adjusted for weeks early) for developmental comparisons.
Related calculators
Sources
- WHO Child Growth Standards — World Health Organization. Effective 01-01-2006, reviewed 13-09-2026.
This calculator provides a general date calculation only and does not constitute personalized medical or developmental advice. Consult your pediatrician for developmental guidance.
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