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Baby Age Calculator
Calculate your infant's exact age in weeks, months, and days from their date of birth. Track developmental milestones and never miss a pediatric appointment date.
Baby Age Calculator
Enter your baby's birth date to calculate their exact age
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Total Weeks
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Total Months
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Total Days
🏁 Developmental Stage Progress
Newborn
3 Mo
6 Mo
12 Mo
2 Yr
Reference Guide
Baby Age Quick Reference Chart
Common baby age conversions — weeks to months to days
| Age (Weeks) | Age (Months) | Age (Days) | Development Stage |
|---|---|---|---|
| 1–2 weeks | 0 months | 7–14 days | 🍼 Newborn |
| 4 weeks | 1 month | 28 days | 🍼 Early Newborn |
| 8 weeks | 2 months | 56 days | 👁️ Social Smiling |
| 12 weeks | 3 months | 84 days | 🗣️ Cooing Begins |
| 16 weeks | 4 months | 112 days | 🤲 Reaching for Objects |
| 24 weeks | 6 months | 168 days | 🥣 Solid Foods |
| 36 weeks | 9 months | 252 days | 🧸 Crawling Stage |
| 52 weeks | 12 months | 365 days | 🎂 First Birthday! |
| 78 weeks | 18 months | 546 days | 🚶 Walking & Talking |
| 104 weeks | 24 months | 730 days | 🎨 Toddler Years |
FAQ
Baby Age Calculator — Common Questions
How do I calculate my baby's age in weeks?
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To calculate your baby's age in weeks, count the number of days from their birth date to today, then divide by 7. For example, if your baby is 56 days old, they are exactly 8 weeks old. Our calculator does this automatically and shows total weeks, months, and days all at once.
How many weeks is 3 months old?
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3 months is approximately 13 weeks (91 days). Because calendar months vary in length (28–31 days), the exact number of weeks depends on which months your baby lived through. Our calculator uses the precise calendar dates to give you an exact week count, not an approximation.
When do doctors switch from weeks to months for baby age?
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Pediatricians typically use weeks for the first 3 months (12 weeks) of a baby's life, then switch to months from 3–24 months, and finally years after age 2. In the NICU or for premature babies, weeks may be used much longer — sometimes up to the corrected age of 2 years.
What is corrected age for premature babies?
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Corrected age (also called adjusted age) is calculated by subtracting the number of weeks premature from your baby's actual age. For example, if your baby was born 8 weeks early and is now 20 weeks old (actual age), their corrected age is 12 weeks. Pediatricians use corrected age to assess milestones in preemies until around age 2.
How many months old is a 1-year-old baby?
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A 1-year-old baby is 12 months old. However, because months have different lengths, a baby who just turned 1 year old could be anywhere from 365 to 366 days old (leap years). After the first birthday, most parents and doctors simply use years and half-years (e.g., "18 months" or "1.5 years").