Babies' Firsts: When babies learn to sit up

A few weeks ago, as part of our Babies’ Firsts series, we asked our readers to answer these questions:

• How old was your baby when he or she was first able to sit up on his or her own?

• How did playtime change once your baby could sit up? 

We’ve gotten several comments from readers, so first we’d like to thank everyone who responded. Each of their babies started sitting up on their own right around 6 months! Not surprisingly, playtime didn’t change much for these babies because they had been sitting up with help, but they were able to play more independently and were showing more interest in toys than they had in the past!

Today, we would like to share what developmental research says about the ages babies tend to learn to sit up. As always, remember that all babies are different and they develop at their own pace. We will provide ranges, but if your baby does not fall in the range, don’t be alarmed. If you are unsure about your baby’s developmental progress, talk to your pediatrician!

Sitting with Support

More than 90% of babies are able to sit up while being held (at the chest/waist) by a caregiver by about 1 month old. In the beginning, the neck muscles are not developed enough to keep the babies’ heads from bobbing around while held in the sitting position, but within the first few months, their necks get stronger and they are better able to control their heads while being held in a sitting position.

Sitting with Propped Arms or Arm Support

Before being able to sit fully upright on their own, many babies can sit while using their arms to support their weight. According to the research, 50% of babies can sit this way by 2.5 to 3 months of age and 90% can sit this way by 4.5 months. This type of sitting shows off babies’ flexibility because they often look like they are folded right in half when sitting this way! Between 4.5 and 6.5 months, their arms get stronger and they are able to sit up higher with their arms closer to their bodies.

Sitting without Arm Support

The age range for the ability to sit without any arm support is much wider. Between 4.5 and 6 months, babies usually begin sitting without their hands or arms on the ground, but as you can imagine, they aren’t able to sit fully upright right away and need to be closely watched to make sure they don’t fall and hurt themselves. As they gain strength, they are able to straighten up more easily, and by 8 months more than 90% can sit up well enough to be left alone in a sitting position.  

Sitting and Moving Around

Once a baby has mastered sitting independently, he or she won’t  sit still for long. Fifty percent of babies can twist and rotate around to reach for things by 7 months and 90% can do this by 8.5 months.  Between 8 and 12 months, they start moving from sitting to lying on their tummies (50% around 8 months and 90% around 12 months), which is an important step to prepare for crawling!

Safety is key!

So, no matter when your baby starts sitting up independently, the most important thing is to keep them safe.  Even when they have been sitting for a while and seem to have mastered the skill, be cautious when sitting them down. Never leave your baby alone on a couch, chair, or bed and keep the floor around your baby clear when he’s playing. For more information on baby proofing, you can review some of our previous posts (click here).