Baby Age Calculator
In the first year of life, pediatricians track infant development in days and weeks rather than months. Enter your baby's age in days to instantly see their age in weeks, months, and hours — useful for growth charts, milestone tracking, and communicating with healthcare providers.
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Formula
Weeks = Baby Age (days) ÷ 7
Dividing days by 7 gives exact weeks (decimal weeks show partial weeks). Dividing by 30.44 (average calendar month) gives age in months. Multiplying by 24 gives the total hours the baby has been alive. Pediatricians use weeks for premature infants and weeks-and-days for all babies in the first few months.
How to use the Baby Age Calculator
- 1
Enter your baby's age (days)
- 2
Read your results instantly
Results update in real time as you type.
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Why Days and Weeks Matter for Infants
In the first few months of life, development moves so quickly that monthly milestones are too coarse. A baby at 6 weeks is developmentally very different from one at 10 weeks. Pediatricians use gestational age (weeks from conception) for premature infants and chronological age (weeks since birth) for full-term babies. Growth charts, vaccine schedules, and developmental milestones are all keyed to week-level precision in the first year.
Corrected Age for Premature Babies
If your baby was born prematurely, pediatricians use 'corrected age' (chronological age minus weeks premature) for developmental comparisons. A baby born 6 weeks early at 60 days old has a corrected age of 60 − 42 = 18 days. This calculator uses chronological age (actual days since birth). Subtract the premature days from your input to get corrected age in weeks.
Tips & Insights
Track Milestones by Week
The CDC and AAP milestone checklists are organized by 2-month increments. At 2 months (about 60 days), your baby should respond to faces; at 4 months (about 120 days), laugh and babble.
Share Weeks with Your Pediatrician
When calling your pediatrician with a concern, stating your baby's age in weeks (e.g., '8 weeks, 3 days') gives more precise clinical context than just saying '2 months.'
Document Weekly Firsts
Keeping a note of firsts (first smile, first laugh) tagged by weeks makes a meaningful record that is also useful at well-baby appointments.
Worked Examples
3-Month-Old Baby (90 days)
12.86 weeks, 2.96 months, 2,160 hours.
Newborn at 2 Weeks (14 days)
2 weeks, 0.46 months, 336 hours.
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Frequently Asked Questions
How do I find my baby's age in days?
Count the calendar days from the birth date to today. Most smartphone calendars can calculate this, or count manually using a wall calendar.
What is corrected age for a premature baby?
Corrected age = chronological age minus the number of weeks premature. A baby born 4 weeks early who is now 8 weeks old has a corrected age of 4 weeks.
When do pediatricians stop counting in weeks?
Most providers switch to months after about 3 months, and to years after 2 years. Exact week counts remain relevant for developmental assessments throughout the first year.
What is the 4-month sleep regression?
Around 16-17 weeks (about 115-120 days), most babies undergo a neurological change in sleep architecture that temporarily disrupts sleep patterns. It is a sign of healthy brain development.
Why does month calculation use 30.44?
Calendar months vary from 28 to 31 days. The average of 365.25 ÷ 12 = 30.44 days per month is used for consistency. For clinical age, healthcare providers use week counts, not months.
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