Most babies can get themselves into a sitting position from lying down by around 9 months old. This is different from sitting upright when placed there, which happens earlier, around 6 to 8 months. The ability to independently push up from the floor into a seated position is one of the later stages of sitting development, and some babies don’t master it until closer to 12 months.
The Stages of Sitting Development
Sitting doesn’t happen all at once. Babies move through a clear progression, and each stage builds on the one before it.
Around 4 to 6 months, babies start “tripod sitting,” where they prop themselves up with both arms in front of them like a little kickstand. They can hold this briefly but topple easily. By 6 to 8 months, most babies can sit steadily without using their hands for support, as long as you place them in that position first. They’re balancing on their own, but they still can’t get there by themselves.
The transition from lying down to sitting, the skill you’re probably watching for, typically appears around 9 months. The CDC lists “gets to a sitting position by herself” as a milestone most babies reach by 9 months. Some babies figure it out a bit earlier, and others take until around 12 months to do it smoothly and consistently without any help.
How Babies Actually Get Themselves Up
Babies don’t do a tiny sit-up from their backs. The movement is more creative than that. Most babies roll onto their stomachs first, push up onto their hands and knees, then shift their weight to one side and swing into a half-sitting position propped on one hand. From there, they push the rest of the way up.
This side-propping transition requires a surprising amount of coordination. Your baby needs to bear weight through one shoulder and arm, bend their trunk to one side, and move each leg independently. Some babies figure out a slightly different route, going from hands-and-knees directly into a sit by dropping one hip to the floor. Either way, crawling position and sitting position are closely linked. Babies who can balance on all fours often start experimenting with sitting shortly after.
What Has to Develop First
The biggest physical prerequisite is trunk control, specifically the ability to stabilize the ribcage over the pelvis. Early in sitting development, babies struggle to coordinate these two parts of their body at the same time. That’s why young sitters wobble and fold forward. The core muscles that connect the upper and lower trunk need months of practice before they’re strong enough to hold everything steady during a complex transition like pushing up from the floor.
Before your baby can attempt this move, they generally need to be comfortable pushing up on straight arms during tummy time (like a cobra pose), holding their head up steadily, and rolling in both directions. These are all signs the neck, shoulder, and core strength is building toward that sitting transition. If your baby isn’t doing those foundational movements yet, the push-to-sit skill is still a few steps away.
How to Encourage the Transition
The single most helpful thing you can do is stop always placing your baby directly into a sitting position. Instead, help them practice the actual movement of getting there. Lay them on their side, then gently guide them to push up through their arm into sitting. This teaches the motor pattern they’ll eventually do on their own.
Plenty of tummy time builds the arm and shoulder strength needed for the push-up portion. Once your baby is comfortable on their stomach, encourage them to push up tall on straight arms. You can help by giving a little boost at the chest, placing them on a slight incline, or using a therapy ball to make pushing up easier and more fun.
When practicing sitting, put toys at eye level rather than on the floor. This encourages your baby to stay upright and reach, which strengthens the trunk muscles that control balance. A play table with the front legs removed creates a nice angled surface for supported sitting practice. The goal is to let your baby move in and out of sitting repeatedly rather than just parking them in one position.
When to Lower the Crib Mattress
Once your baby can sit up on their own, the crib becomes a different safety equation. A baby who can push to sitting can also start pulling on the crib rails, and a mattress set too high turns into a fall risk. Pediatricians recommend moving the crib mattress to its middle setting as soon as your baby can sit up independently, commando crawl, or get up on hands and knees. For most babies, this happens around 6 months.
By the time your baby can pull to standing (typically around 9 months), the mattress should be at its lowest setting. Keep the crib free of pillows, blankets, stuffed animals, and bumpers during the entire first year, and always place your baby on their back to sleep, even once they can sit and roll freely.
Signs of a Possible Delay
There’s a wide range of normal for sitting milestones, so a baby who’s a month or two behind the averages isn’t necessarily delayed. That said, difficulty with rolling over, sitting up, and other gross motor skills can sometimes signal a developmental delay worth investigating. If your baby can’t sit with support by 9 months, can’t get into a sitting position at all by 12 months, or has lost sitting skills they previously had, those are worth bringing up with your pediatrician. Delays in one motor area often respond well to early intervention, particularly physical therapy tailored to infants.