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When do babies sit up?

When do babies sit up?

At what age will your baby be able to sit? When will they be able to sit without support? Our expert GP explains what to expect when – and what you can do to encourage your baby to learn to sit

6 months old baby sitting up unaided

Dr Philippa Kaye

Published: October 31, 2023 at 4:02 PM

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Sitting up is a major developmental milestone in your baby's life and, as with other key gross motor skills – like crawling, pulling up to standing and walking – your baby may learn to sit before or after other babies of the same age.

Learning to sit is actually a process that your baby masters in several mini-stages – from starting to sit up, to being able to sit supported to being able to sit up on their own.

Here's what you need to know about each of those stages, at what age each is likely to happen – and what you can do to help your baby practise sitting and strengthen the muscles that will, in time, help them sit unassisted. Wondering when your baby's babbles will turn into proper words discover our baby's first words guide to first words and milestones.

At what age do babies start to sit up?

Generally speaking, at about 4 or 5 months, a baby will be able to sit supported in an adult's lap or with pillows propping them up. This is called 'passive sitting'.

By about 6 months, most babies can manage some 'active sitting', either using one or both of their own arms for support (sitting in what's call the tripod position, like the baby in our picture) or even sitting entirely unsupported – but usually only for a few seconds.

As your baby's core muscles get stronger, their balance and stability will improve and they will gradually be able to sit unsupported for longer. Usually, by about 8 to 10 months, your baby will be able to sit independently. This often coincides or overlaps with your baby starting to crawl.

How will my baby learn to sit up?

Learning to sit up is a multi-stage process that progresses as your baby develops not just muscle strength but coordination an cognitive skills in these key areas:

First, your baby learns how to hold up their own head. By about 3 months, your baby should be able to hold their head up when you hold them upright against your shoulder.
Then, head control improves and back muscles strengthen. From around 3 months to 4 months, your baby should be able to control their head as you pull them up from a lying-down position into a sitting position. And when you put your baby on their tummy, they'll start to lift their head from the floor to look horizontally ahead.
Then core muscles strengthen and the brain 'understands' sitting. At 4 months to 5 months, if your baby's on their tummy, they should be able to lift their head, hold it steady and look around. They'll also be able to do 'mini push-ups', propping themselves up on their arms and pushing their chest off the floor.
Then, by at 6 months, their back muscles are likely to be strong enough to support them sitting supported – propped with cushions in the corner of the sofa, for example – for short periods. This nicely strengthens their trunk muscles, and helps your baby get used to the feeling of sitting.
Then your baby starts to gain balance and stability. From 5 to to 6 months, As your baby learns to sit independently, they'll put one or both arms on the floor to stabilise their torso and stop themselves toppling over. This is called the tripod sitting position.
Gradually, your baby will gain more control of their core muscles. From around 8 months, they should be able to sit for longer and to sit more upright. Over the next weeks, they'll develop enough balance in the sitting position to be able to reach for toys and, eventually, rock forwards and backwards to get on their hands and knees.

How can I help my baby learn to sit up?

As soon as your baby can hold their head well, there are lots of things you can do to encourage your baby to strengthen their muscles for sitting – and to develop the brain connections that spur their desire to sit.

Encourage lots of tummy time. Time lying on, and eventually pushing up from, their tummy (on a blanket or a playmat) allows your baby develop strength in their neck and core muscles. Start with 5 minutes a day, building up to 20 to 30 minutes a day by the time your baby is 3 to 4 months old.
Let your baby play on their back too – all that kicking and arm-waving, and maybe even rolling, is brilliant all-over muscle-strengthening stuff.
From about 4 months, place your baby on their back, hold their hands and gently pull them up to sitting. They should be able to keep their head steady and level – and may even brace their neck.
Once your baby can push up on their arms from a tummy-down position, you can introduce them to sitting. Place them on your lap facing away from you with their head and neck leaning again your chest. Do this in short bursts – for maybe 5 to 10 minutes at a time, a few times a day. Gradually, you can try offering slightly less support: place them facing towards you instead, with your hands holding the middle of their trunk, then, as their back muscles get stronger, move your hand to offer support further down, by their hips.
Sit your baby on the floor or in the corner of sofa, supported by cushions and/or a play ring or a breastfeeding support pillow. Again, aim for short bursts, a few times a day. (And obviously, don't leave your baby unsupervised, especially if they're up on a sofa.)
Sit your baby between your legs. Sit on the floor with your back supported and your legs wide apart. Place your baby between your legs, so that your body (or your arms) can support their body if it goes a bit wobbly. Offer your baby toys to hold or to pick up from the floor, so they can practise moving their arms while sitting.

Remember: babies are naturally wired to learn to sit. So, as long as you encourage your baby's natural urges to move, strengthen their muscles and refine their motor skills, they'll get there at their own pace. Hard as it might be, don't compare your baby to other babies: every one reaches this key developmental milestone at their own pace.

Is it safe to use infant floor seats for my baby to practise sitting?

Yes, but not not for extended periods of time. These moulded seats can be super-useful – and babies do often enjoy sitting in them – but because their purpose is to keep your baby stable, they can limit your baby's natural movement. If your baby spends too much time with their movement limited in this way, it may interfere with the development of their independent sittings kills.

When can my baby sit in a highchair?

Once your baby can sit independently, you can sit them in a highchair. Make sure the highchair has a footrest and a tray (or tabletop) for resting their arms. This way, your baby can align and support their torso, relieving any strain on their spine.

When should I worry that my baby’s not sitting up yet?

If your baby is not sitting by 9 to 12 months, then please talk to your doctor.

What is the difference between passive sitting and active sitting?

Passive sitting is supported sitting: when your baby sits on someone's lap, for example, or is propped up in a sitting position with cushions or a moulded baby seat. Passive sitting is brilliant for giving your baby a sense of all that sitting offers but it's important not to keep your baby sitting passively for extended periods – they can get tired and cranky, if they're not developmentally ready to sit for long and if they don't have any opportunity to wriggle or move on their own.
Active sitting is sitting independently: when your baby sits without needing support or without holding themselves up with their hands. A baby who can sit actively has relatively good stability in their baby's spine and back muscles but it's worth knowing that their spine is still quite rounded, compared to an adult's. For this reason, it's best not to keep your baby in a sitting position for hours and hours.

With thanks, for additional material, to our colleagues at Netmoms, Germany

Pic: Getty Images

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Authors

Dr Philippa Kaye

Dr Philippa KayeGP

Dr Philippa Kaye is a GP, media doctor and author with a particular interest in women's, children's and sexual health. She has written multiple books including The Science of Menopause, Breasts: An Owner's Guide and Doctors Get Cancer Too, her memoir of being 39 years old, a busy doctor and mother when she was diagnosed with bowel cancer.