Baby Age Calculator
Calculate your baby's exact age in weeks, months, and days
What Is a Baby Age Calculator?
A baby age calculator is a specialized tool that calculates your baby's exact age in multiple formats – weeks, months, and days. Unlike standard age calculators, this tool is specifically designed for infants and toddlers, providing the precise measurements parents and pediatricians use to track development.
Baby age calculators are essential for:
- Tracking developmental milestones: Know when to expect rolling, crawling, walking, and talking
- Pediatric appointments: Doctors track baby development by weeks and months
- Growth monitoring: Compare your baby's progress to standard growth charts
- Vaccination schedules: Immunizations are given at specific ages in weeks/months
- Sleep patterns: Sleep needs change dramatically in the first year
- Feeding guidelines: Know when to introduce solids and adjust feeding schedules
How to Calculate Baby's Age in Weeks
Calculating your baby's age in weeks is straightforward:
- Enter birth date: Select your baby's date of birth
- Select calculation date: Choose today or any specific date
- Click calculate: Get instant results in weeks, months, and days
Formula: Baby's age in weeks = (Current date - Birth date) ÷ 7
During the first 12 weeks (3 months), pediatricians typically track age in weeks. After that, age is usually measured in months until the baby turns 2 years old.
Baby Developmental Milestones by Age
Newborn (0-3 Months / 0-12 Weeks)
- Physical: Lifts head briefly, begins tracking objects with eyes
- Social: First social smiles (6-8 weeks), responds to voices
- Motor skills: Grasps reflexively, brings hands to mouth
- Communication: Coos and makes gurgling sounds
- Sleep: 14-17 hours total, waking every 2-3 hours to feed
Young Infant (3-6 Months / 12-26 Weeks)
- Physical: Rolls over (4-6 months), sits with support
- Social: Laughs out loud, recognizes familiar faces
- Motor skills: Reaches for and grabs objects, brings toys to mouth
- Communication: Babbles with consonant sounds ("ba-ba-ba")
- Sleep: 12-16 hours total, may sleep through the night
Older Infant (6-12 Months / 26-52 Weeks)
- Physical: Sits without support (6-7 months), crawls (7-10 months), stands with support (9-12 months)
- Social: Separation anxiety begins, plays peek-a-boo
- Motor skills: Pincer grasp (picks up small objects), transfers objects between hands
- Communication: First words (10-14 months), understands "no"
- Feeding: Starts solid foods (6 months), self-feeding finger foods
Toddler (12-24 Months)
- Physical: Walks independently (12-15 months), runs (18 months), climbs stairs
- Social: Shows affection, plays alongside other children (parallel play)
- Motor skills: Stacks blocks, scribbles with crayons, drinks from a cup
- Communication: Vocabulary explosion (50+ words by 18 months, 200+ by 24 months)
- Sleep: 11-14 hours total, transitions to one nap per day
How to Convert Baby Weeks to Months
Converting weeks to months for babies is not exact because months have varying lengths:
| Weeks | Approximate Months | Milestone Period |
|---|---|---|
| 0-4 weeks | 1 month | Newborn |
| 4-8 weeks | 2 months | First smiles |
| 8-13 weeks | 3 months | Head control improves |
| 13-17 weeks | 4 months | Rolls over |
| 17-22 weeks | 5 months | Sits with support |
| 22-26 weeks | 6 months | Solid foods begin |
| 26-30 weeks | 7 months | Sits independently |
| 30-35 weeks | 8 months | Crawls |
| 35-39 weeks | 9 months | Pulls to stand |
| 39-43 weeks | 10 months | Cruises (walks holding furniture) |
| 43-48 weeks | 11 months | Stands alone briefly |
| 48-52 weeks | 12 months (1 year) | First steps |
Baby Growth Tracking by Age
Pediatricians track baby growth using standardized percentile charts. Here's what to expect:
Average Growth Rates
- Birth to 3 months: Gains 5-7 oz per week, grows 1-1.5 inches per month
- 3-6 months: Gains 4-5 oz per week, grows 0.5-1 inch per month
- 6-12 months: Gains 2-4 oz per week, grows 0.5 inch per month
- Weight milestones: Doubles birth weight by 5 months, triples by 12 months
- Length milestones: Grows approximately 10 inches in first year
Head Circumference
- Birth: Average 13.5 inches (34-35 cm)
- First 3 months: Grows 2 cm per month
- 3-6 months: Grows 1 cm per month
- 6-12 months: Grows 0.5 cm per month
Baby Vaccination Schedule by Age
Immunizations are given at specific ages. Here's the standard CDC schedule:
- Birth: Hepatitis B (1st dose)
- 2 months (8 weeks): DTaP, Hib, IPV, PCV, Rotavirus, Hepatitis B (2nd)
- 4 months (16 weeks): DTaP, Hib, IPV, PCV, Rotavirus (2nd dose)
- 6 months (26 weeks): DTaP, Hib, IPV, PCV, Rotavirus (3rd), Hepatitis B (3rd), Flu (annual)
- 12-15 months: MMR, Varicella, Hepatitis A (1st), PCV (4th), Hib (4th)
- 18 months: DTaP (4th), Hepatitis A (2nd)
Baby Feeding Guide by Age
0-6 Months
- Exclusive breastfeeding or formula: Every 2-3 hours (8-12 times per day)
- Amount (formula): 2-3 oz per feeding (newborn), increasing to 6-8 oz by 6 months
- No solid foods: Digestive system not ready
6-8 Months
- Breast milk/formula: Still primary nutrition (24-32 oz per day)
- Solid foods: Introduce single-ingredient purees (rice cereal, vegetables, fruits)
- Frequency: 2-3 solid meals per day
8-12 Months
- Breast milk/formula: 24-30 oz per day
- Solid foods: Soft finger foods, mashed table foods, variety of textures
- Frequency: 3 meals + 2 snacks per day
Baby Sleep Patterns by Age
Newborn (0-3 Months)
- Total sleep: 14-17 hours per day
- Pattern: Irregular, wakes every 2-3 hours to feed
- Naps: 4-5 naps per day
Young Infant (3-6 Months)
- Total sleep: 12-16 hours per day
- Night sleep: 6-8 hour stretches possible
- Naps: 3-4 naps per day (2-3 hours total)
Older Infant (6-12 Months)
- Total sleep: 12-15 hours per day
- Night sleep: 10-12 hours (may sleep through night)
- Naps: 2-3 naps per day (2-3 hours total)
Toddler (12-24 Months)
- Total sleep: 11-14 hours per day
- Night sleep: 10-12 hours
- Naps: 1-2 naps per day (1.5-3 hours total)
People Also Search For
Baby age in weeks calculator?
To track your baby's age in weeks — the standard unit used by pediatricians during the first three months — enter your baby's birth date in the calculator above and it will instantly show the total weeks old your baby is. Weeks are the preferred measurement during the newborn and young infant stages because development happens so rapidly; a 4-week-old and a 10-week-old are at very different developmental stages even though both are technically "under 3 months old."
How old is my baby in months?
Enter your baby's birth date in the calculator to get the exact age in months, weeks, and days — for example, "4 months, 2 weeks, 3 days." Babies grow and develop differently at each month, so knowing the precise age in months helps parents match their baby to the right developmental milestone guides, feeding schedules, and vaccination timelines used by pediatricians.
How to calculate corrected age for premature babies?
Corrected age (also called adjusted age) accounts for prematurity: subtract the number of weeks born early from your baby's actual age. For example, if your baby was born 6 weeks early and is now 16 weeks old (actual age), the corrected age is 10 weeks (16 − 6 = 10). Corrected age is used when tracking developmental milestones until about 2 years old. Always consult your pediatrician for personalized guidance on using corrected vs. actual age for your baby's specific situation.
Baby milestones by age in months?
Key developmental milestones by month include: social smiling around 2 months, rolling over at 4–6 months, sitting independently at 6–8 months, crawling at 7–10 months, first words around 10–12 months, and walking at 12–15 months. The baby age calculator helps you track exactly which milestone window your baby is currently in based on their precise age in weeks and months — so you know what to look for and when to flag any concerns with your pediatrician.
How many weeks old is my newborn?
Enter your baby's birth date above and the calculator will tell you exactly how many weeks and days old your newborn is — this is one of the most common questions parents bring to pediatrician visits in the first three months. Knowing the exact week matters for following feeding guidelines, understanding sleep patterns, and determining when vaccinations are due, since the early immunization schedule is based on age in weeks (2 months = ~8 weeks, 4 months = ~17 weeks).
When does a baby stop being counted in weeks?
Pediatricians typically stop counting age in weeks at around 3–4 months (12–16 weeks), then switch to months until the child turns 2 years old, after which years are used. This progression reflects how quickly development changes: in the first weeks, even a few days matters; by the toddler stage, month-to-month differences are more meaningful. Some parents and doctors continue using weeks informally up to 6 months, especially for premature babies who may be tracked on an adjusted age schedule longer.