Your 15 Week Old Baby: Every Milestone You Should Look For

Your baby's sleep could be about to change again!

Your tiny baby is now just over 3 months old!

Your little one is out of the newborn stage now and is developing rapidly. A lot will have already changed since those hazy early days, your baby has a lot more energy now and will be much more alert, you may have noticed they are easily distracted too!

Quite a few major milestones are on the horizon now, including teething, the 4 month sleep regression, some big leaps and growth spurts and not to mention lots of smiles and giggles. We have gathered up some key 15-week-old baby milestones to look out for and added some tips about how to deal with the trickier aspects, along with some fun activities to encourage development.

As your baby is getting older, you might be interested in reading about a [6-month-old schedule] and the potential 6 month sleep regression.


Your little one is going through some major developmental leaps at the moment, and a key part of this is that their sleep patterns begin to change and mature. They will now start to experience light and deep sleep cycles just like us. Here are our top tips to try to manage a 15-week-old's sleep:

At just over 3 months old, your baby needs around 15 hours sleep within a 24 hour period. This includes naps, and your baby probably still needs three naps a day. Keeping your 15-week-old baby sleep routine the same is key with a regression. Babies love routine as it helps them feel secure, so with all these new abilities and changes, they will love the familiarity of their bath, cuddle, feed, bedtime with you each night.

Bedtime needs to be extra calm and taken at a slow pace, for now, we want to give their busy brain a chance to rest, so dim lighting and calming vibes should help.

Baby is noticing everything at the moment.


At 15 weeks your baby's diet will still be exclusively breast milk or formula. By now you may have found a comfortable routine, and hopefully, if you are breastfeeding your baby will have a great latch, and the initial discomfort for you should have subsided. If you do have any concerns with your baby's feeding, such as if they struggle to latch on or don't seem satisfied after a feed (breast or bottle), be sure to speak to your doctor. Feeds are often around every three to four hours but don't worry if baby veers slightly from this. Here are our top feeding tips:

At this stage in 15-week old baby development, you will notice your baby gets distracted a lot! So when it comes to feeding, there will be some starting and stopping and a lot of head turning. During the day you might find they are pretty much drinking the bare minimum they need to be satisfied, and catching up at night instead.

If you are breastfeeding, don't worry about these changes as your breasts will adjust to what your baby is telling them, you may feel uncomfortable at times as bigger feeds are now shorter but it will balance out.

With a formula-fed baby you will see very similar distracted behavior. Although it can be a little frustrating that feeds take longer now, don't be tempted to prop your baby's bottle up. This can be a major choking hazard and prevents you from engaging with them and noticing their cues for when they need to stop.

At this age, your baby's weight should be going up steadily. At 3.5 months the average 15-week old baby weight is 14.1 lbs for a boy and 13 lbs for a girl, according to the WHO. Breastfed babies will usually gain weight at a slower pace than formula-fed babies, as when bottle-feeding, we often unintentionally encourage baby to finish the whole bottle, even though they may not need that much milk at the time. It can help to look out for cues as to when your baby is hungry and when they've had enough.

As long as your baby is steadily gaining weight, their body will be getting everything they need from either breast milk or formula.  Their stomachs aren't ready for solid food yet, so hold off until 6 months unless told otherwise by your pediatrician.

Baby's neck and core muscles are getting stronger every day.

Play & Movement

Your baby is so alert now and will be really responsive to bright colors, sensory activities, and music. You might decide to include some fun baby classes into your 15-week-old baby schedule, your little one will also love the chance to see other babies.

Your little one's neck control will be improving by the day, especially if you've been letting them get plenty of tummy time. They will be able to turn their head when they hear something of interest, and you will notice them following your movements and observing you carefully. Here are our top play and movement tips:

A big milestone that you could be seeing soon is learning to roll over! This is really exciting for your baby and once they manage it, it's going to be hard to stop them rolling over all the time, so make sure they have plenty of space to roll and a lot of supervision. If your baby isn't rolling over don't fret, they are still developing muscles and they all do things in their own time.

Your baby might start rolling over when they sleep, and they might start to try and sleep this way. The risk of SIDS is increased when babies sleep on their fronts, so to be safe, keep your baby sleeping on their back.

At 15 weeks your baby is easily overstimulated, it is really important to find a balance between exciting activities, and time to relax and be calm. If your baby is turning away, getting fussy, or closing their eyes, these are signs they've had enough. Lots of cuddles and kisses help your baby feel secure and safe in between the busier playtimes.


As we've mentioned above, your baby's vision has been going through some major development, which is why they are noticing everything at the moment! Their other senses are now joining in and smells, sights, textures, and sounds are being pieced together to create their sensory network.

Parenting at this age is especially rewarding as you can really see how your baby is growing and developing every single day, there are lots of activities you can do to help your baby learn how their senses work. Don't forget about overstimulation and remember if your baby is rubbing their eyes and looking away, they need a break. Here are our top tips:

Talking to your baby and mentioning their name a lot will encourage speech and understanding, and learning who they are!

Even though your baby is still very young, reading with them is so important as not only is it a wonderful bonding activity, but hearing lots of different words and learning to associate those words with the pictures they can see, creates an amazing basis for both speech and thought development.

Your baby is discovering parts of their body and figuring out how they work, hand- eye coordination is improving all the time. They will be able to grab things soon if not already, and you can bet everything is going straight in their mouth so watch out for that!

Now their vision is getting clearer, your baby is starting to notice different colors and they will probably enjoy looking at different patterns and bold picture books now. A baby gym where they can look up at colorful soft toys, and reach out to grab scrunchy sensory toys is a great activity for them.

Anything Else To Look Out For

Now that your little one is 15 weeks old, you will probably have a pretty good idea of what is 'normal' for your baby, so if anything ever seems out of the ordinary or you have concerns about their behavior, mood, temperature, or anything at all, trust your instincts and contact your doctor.

If you found this article helpful, then why not take a look at our sample [5-month-old sleep schedules] or 7-month-old schedules for more information about under ones?


Written By

Amy Lines

Freelance writer Amy lives in Hampshire with her 3 year old daughter, who is a super energetic, chatty child, leading to Amy’s interest in all matters to do with infant and child sleeping patterns and mindfulness for adults and children. Amy’s degree was in fashion design and she loves filling their beautiful home full of interesting textiles, tiles, art, ceramics, and houseplants or, alternatively, pining over them on Instagram. When they aren’t out exploring in the fresh air they can be found cosying up at home, painting, knitting, and dancing!

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