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How Many Bones Does a Baby Have?

Medically Reviewed by Dr. Leah Alexander, MD, FAAP
You’ll be surprised about how many bones does a baby has.

If you have ever wondered, “How many bones does a baby have?”, don’t worry. You’re not alone. It seems like a question best suited for a tricky trivia contest.

Most of us would assume if asked, that babies have the same number of bones as adults. Some of us would know that the bone plates of a baby’s skull have yet not fused, so, technically, their skull has more bones than that of an adult. But, few people actually know that babies have more bones overall.

Yes, you read that right, babies have more bones than adults.

Way more. Let me explain.

Key Takeaways

  • Babies have 300 bones at birth, which is almost 100 more bones than an adult’s 206 bones.
  • Many of a baby’s bones are made of softer cartilage, allowing them to be flexible for growth and passing through the birth canal.
  • Baby bones eventually harden and fuse together to form the 206 bones an adult has by early adulthood, around 20 to 25 years.
  • Good nutrition and weight-bearing exercises help babies develop strong, healthy bones as they grow.

How Many Bones Do Babies Have At Birth?

You may already know that an adult has 206 bones, but we are actually born with 300 bones (1).

How is this possible? Shouldn’t a baby have the same number of bones as an adult?

Or, why wouldn’t a baby have fewer bones than an adult at birth?. Infants have less hair and fewer teeth, so why would they have more bones?

Why Do Babies Have More Bones Than Adults?

Our skeleton does not start out as the hard, rigid set of bones that we have as an adult. Instead, the first bones are primarily of soft cartilage.

In the womb, babies have a limited amount of space to grow. They also must be flexible in order to pass through the birth canal. So, at birth, many of a baby’s bones are still predominantly made of cartilage (2). For example, cartilage is the firm but flexible material that forms your ear.

As we grow, these smaller, softer cartilage bones harden and fuse together, resulting in the 206 bones we have as an adult.

A good example of this is the baby’s skull. At birth, the skull consists of five different plates of bone (3). These plates develop from softer cartilage, and with good reason.

During birth, a baby is pushed down the birth canal by strong muscular contractions. If the skull were the solid, hardened bone that we have as adults, the contractions could crush the skull, causing irreparable damage.

Instead, the five soft plates can be squeezed together, overlapping to allow the baby’s head to emerge without damage.

This is why you can feel the soft spots at the top and back of a baby’s skull. These soft spots, called fontanelles, will slowly grow together and harden. The posterior fontanelle on the back of the baby’s head closes within the first few months of life. The larger, anterior fontanelle, closes between 13 to 24 months old (4).

What Extra Bones Do Babies Have?

Babies have a total of 300 bones, but they are some that have not yet fused or fully developed.

Using the example of the skull again, the five plates of bone that fuse together are pieces of one single bone. So, babies do not truly have extra bones. They have the same bones as an adult, but those bones are in smaller pieces.

When Do Babies Bones Harden After Birth?

First, let’s talk about bone density. You may have heard of the bone density tests recommended for adults over the age of 65. Density refers to the amount of calcium and minerals that are stored within bones, giving them strength. The greater the amount of stored calcium, the harder the bone.

The calcium in breastmilk or formula helps the bones of infants to transition from mostly cartilage to a more solid form (5). As a child grows, dietary calcium continues to be important. Vitamin D from supplements or skin exposure assists with bone absorption of this calcium (6).

Because hardened bones cannot grow, the ends of our bones contain softer growth plates made of cartilage. In this way, bones can lengthen throughout a child’s life, and continue to support and protect their bodies. In girls, growth plates typically fuse a few years after the first menstrual period, around ages 13 to 15. For boys, their growth plates fuse much later, after age 17 (7).

Growth plates finally harden somewhere between the ages of 20 and 25. After this point, our bones can no longer grow.

The clearest example of this is the fontanelle of the skull. Your baby’s skull bones are slowly hardening from the moment they are born, and fuse to close the fontanelles. However, this malleability and slow hardening may come with problems.

In keeping with the skull example, you may have noticed an infant with flattening on the back or one side of the head. This results from frequent pressure on these parts of the head, typically from lying flat for extended periods of time (8). Fortunately, because the skull bones are malleable, the misshapen head can improve with more tummy time or another positioning.

Bone malleability can also be positive if your child is born with a misshapen one. For example, some babies are born with a foot that appears more flexed than the other, usually because of intrauterine positioning (9). Most cases will self-resolve as the foot bones grow. In others, it is possible to direct the growth of that bone into a more regular shape as the baby grows.

At What Age Do You Have 206 Bones?

The exact age at which you have 206 bones varies from person to person, but this normally happens by early adulthood, or around 20 to 25 years (10).

By this time, the cartilaginous growth plates at the ends of the bones have hardened, and they can no longer grow.

However, although your bones do not grow in size, they continuously remodel throughout your lifetime (11).

How to Protect Your Baby’s Bones

Once your baby is born, the best thing you can do for their skeletal system is to ensure they eat well, and have good, balanced nutrition.

One of the most important vitamins for bone health is vitamin D. Babies who are fed with formula usually receive enough of this vitamin.

Take Note

However, babies who are exclusively breastfed may need a vitamin D supplement (12). This is true even if the baby’s mother is taking supplements herself which includes vitamin D. Allowing your baby a few minutes of sunlight per day may help, but a supplement is still recommended.

Once your baby begins to eat solid food, they will need a diet with plenty of vitamin D and calcium.

Calcium-rich foods include (13):

  • Dairy products.
  • Some fish, such as sardines, salmon, and trout.
  • Green vegetables like spinach, kale, okra, and collards.
  • Soy products
  • Sesame

Vitamin D rich foods include (14):

  • Fatty fish such as mackerel, salmon, and tuna. Be careful of which kinds of fish you give your child. Some have potentially high mercury levels (15).
  • Egg yolks.
  • Vitamin D enriched foods.

In addition to “feeding” your child’s bones, you can help strengthen them by encouraging your child to take part in weight-bearing exercise. Activities such as running, jumping, and climbing put weight on the bone, which helps the body build stronger bones.

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Boning Up on Your Baby’s Anatomy

Your baby is not only the most beautiful child in the world, but they are also an amazing collection of soft, springy bones that will harden and fuse over time to create a strong, sturdy adult skeleton.

You can help with this process by encouraging good nutrition and weight-bearing exercises. Together, this r will set your child up for a lifetime of strength.

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Headshot of Dr. Leah Alexander, MD, FAAP

Medically Reviewed by

Dr. Leah Alexander, MD, FAAP

Leah Alexander, M.D. FAAP is board certified in General Pediatrics and began practicing pediatrics at Elizabeth Pediatric Group of New Jersey in 2000. She has been an independently contracted pediatrician with Medical Doctors Associates at Pediatricare Associates of New Jersey since 2005. Outside of the field of medicine, she has an interest in culinary arts. Leah Alexander has been featured on Healthline, Verywell Fit, Romper, and other high profile publications.