Baby Age Calculator
See how many weeks and months old your baby is, what stage they’re in, and which milestone is coming next.
Defaults to today for real-time updates.
Age Overview
Exact age (as of November 25, 2025)
0 year(s), 0 month(s), 0 day(s)
0 days • 0.0 weeks
Growth stage
Newborn
Next milestone week: 4 (in 4 week(s))
How to Use This Calculator
Enter the birth date
Use the baby’s exact birth date. The tool converts it into days, weeks, and months of life so far.
Track on any day
Leave the reference date as today or set it to a future check-up, travel date, or developmental test.
Monitor milestones
See current stage and upcoming milestone week to prepare for growth spurts, doctor visits, or photography sessions.
Formula
Days Old = floor((Reference − Birth) ÷ 86,400,000 ms)
Weeks = Days ÷ 7
Months ≈ Days ÷ 30.4375
Stage = classify(Weeks)
Example: 150 days old → 21.4 weeks (~5.0 months). Stage: 4-6 months with milestone week 26 upcoming.
Care & Tracking Tips
Growth happens fast! Knowing exact weeks helps align with pediatric guidelines, vaccination schedules, and growth charts.
- Record weight/height alongside the age results after pediatric visits.
- Set reminders for upcoming milestone weeks to review development checklists.
- Capture photos or journal entries each month to watch progress over time.
- Share the week-based age with caregivers so routines stay in sync.
Frequently Asked Questions
Does this adjust for premature births?
For adjusted age, subtract the number of weeks early from the current age. You can add that manually to the output.
What about leap years?
All calculations use actual calendar days, so leap years are handled automatically.
Can I add multiple children?
Run the calculator for each child and save the results. Consider bookmarking each profile separately.
Are milestone names universal?
Stages are generalized. Consult your pediatrician for personalized guidance based on your baby’s development.