Average Baby Weight by Month: A Complete Guide for New Parents

Understanding your baby's growth is one of the most important parts of parenting in the first year. One of the key indicators of a baby’s health and development is weight gain. While every child grows at their own pace, tracking average baby weight by month helps caregivers recognize healthy patterns and identify any potential concerns early.

In this article, we’ll explore the average baby weight by month for boys and girls, factors that influence growth, and tips for encouraging healthy development.

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Why Baby Weight Matters

Babies double their birth weight by 5 months and triple it by their first birthday. Steady weight gain is a sign that your baby is feeding well, growing properly, and developing healthily.

Doctors use growth charts, created by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), to assess if your baby is on the right track. These charts take into account a range of normal weights and lengths for babies of each age and gender.

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Average Baby Weight at Birth

Most full-term babies (born between 37 and 42 weeks) weigh between 2.5 kg to 4.5 kg (5.5 lbs to 10 lbs) at birth.

• Boys: Average 3.4 kg (7.5 lbs)

• Girls: Average 3.2 kg (7.1 lbs)

Babies often lose about 5–10% of their birth weight in the first few days but regain it by the second week.

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Average Baby Weight by Month

Here is a month-by-month breakdown of average baby weight in the first year:

1. 1 Month Old

• Boys: 4.5 kg (9.9 lbs)

• Girls: 4.2 kg (9.2 lbs)

Most babies gain around 150–200 grams (5–7 oz) per week in the first month. Their feeding frequency is high, whether breastfed or formula-fed.

2. 2 Months Old

• Boys: 5.6 kg (12.3 lbs)

• Girls: 5.1 kg (11.3 lbs)

At this stage, babies become more alert and start gaining about 900 grams (2 lbs) a month.

3. 3 Months Old

• Boys: 6.4 kg (14.1 lbs)

• Girls: 5.8 kg (12.8 lbs)

Your baby may begin to hold their head up and smile more. Weight gain remains consistent and steady.

4. 4 Months Old

• Boys: 7.0 kg (15.4 lbs)

• Girls: 6.4 kg (14.1 lbs)

By this time, babies may have doubled their birth weight. Regular pediatric checkups ensure growth is on track.

5. 5 Months Old

• Boys: 7.5 kg (16.5 lbs)

• Girls: 6.9 kg (15.2 lbs)

Babies become more active, rolling and attempting to sit. Growth continues at a healthy pace.

6. 6 Months Old

• Boys: 7.9 kg (17.4 lbs)

• Girls: 7.3 kg (16.1 lbs)

Many babies start trying solid foods now. Breastmilk or formula remains the primary source of nutrition.

7. 7 Months Old

• Boys: 8.3 kg (18.3 lbs)

• Girls: 7.6 kg (16.8 lbs)

Motor skills improve, and your baby may start crawling. Weight gain slightly slows down as they become more mobile.

8. 8 Months Old

• Boys: 8.6 kg (18.9 lbs)

• Girls: 7.9 kg (17.4 lbs)

Teething might begin, and eating habits may vary. Growth remains steady but less rapid.

9. 9 Months Old

• Boys: 8.9 kg (19.6 lbs)

• Girls: 8.2 kg (18.1 lbs)

At this age, babies are more curious and may show food preferences. Daily activity increases, slightly slowing weight gain.

10. 10 Months Old

• Boys: 9.2 kg (20.3 lbs)

• Girls: 8.5 kg (18.7 lbs)

Babies may start standing or cruising. Caloric needs increase, and meals become more diverse.

11. 11 Months Old

• Boys: 9.4 kg (20.7 lbs)

• Girls: 8.7 kg (19.2 lbs)

Solid food intake rises, but breastmilk/formula is still important. Weight gain slows but continues steadily.

12. 12 Months Old (1 Year)

• Boys: 9.6–10.2 kg (21–22.5 lbs)

• Girls: 8.9–9.6 kg (19.5–21 lbs)

Most babies triple their birth weight by their first birthday. They are now eating 3 main meals a day with snacks.

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Factors Affecting Baby Weight

While these averages provide a general idea, several factors influence your baby’s weight:

1. Genetics

Parents’ height and build can affect the baby’s size and growth pattern.

2. Feeding Method

Breastfed babies may gain weight more slowly than formula-fed ones, but both are normal.

3. Health Conditions

Premature birth, infections, or digestive issues can affect weight gain.

4. Activity Level

Babies who are more active may burn more calories, resulting in slower weight gain.

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Signs of Healthy Weight Gain

Here are some signs that your baby is growing well:

• Regular wet diapers (6 or more a day)

• Active and alert behavior

• Meeting developmental milestones

• Doubling weight by 5–6 months

• Tripling weight by 12 months

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When to Be Concerned

Talk to your pediatrician if:

• Baby is not gaining weight or is losing weight after the first two weeks

• Growth percentile drops drastically

• Feeding is difficult or baby seems lethargic

• Fewer than 4–5 wet diapers a day

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How to Support Healthy Baby Growth

Here are tips to encourage healthy weight and development:

1. Frequent Feeding

Feed your baby on demand, especially in the early months. Babies often need 8–12 feedings per day.

2. Monitor Growth

Attend regular checkups to track growth using WHO or CDC growth charts.

3. Introduce Nutritious Solids

At 6 months, start with iron-rich foods like cereals, pureed meats, and vegetables.

4. Respond to Hunger Cues

Pay attention to signs of hunger and fullness. Overfeeding can lead to problems later.

5. Encourage Activity

Tummy time and gentle play build strength and motor skills.

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Final Thoughts

Every baby is unique. While the average baby weight by month offers a useful guideline, healthy growth comes in many sizes and speeds. The key is consistent growth, not matching exact numbers. With love, good nutrition, and regular pediatric visits, your baby is likely to thrive.

If you ever have concerns about your child’s weight or growth, don’t hesitate to speak with your pediatrician. Trust your instincts—you know your baby best.

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