Overtired or Undertired? How to Tell What Your Baby Really Needs
By Chloe Roche, Certified Infant & Child Sleep Consultant and Founder of Sleep Again
“Why won’t my baby sleep?”
If I had a dollar for every time a parent asked me this, I’d probably be writing this blog from a beach somewhere!
One of the biggest reasons babies struggle to settle is that their sleep timing isn’t quite right.
Sometimes they’ve been awake for too long and are overtired.
Other times, they simply aren’t tired enough yet.
And here’s the tricky part…
Overtired and undertired babies can sometimes look surprisingly similar.
So how do you work out which one you’re dealing with?
Let’s take a closer look.
What Does “Overtired” Actually Mean?
Overtiredness happens when your baby has been awake for longer than their body can comfortably manage.
As babies become tired, they can show changes in behaviour such as fussiness, clinginess, yawning, staring into space, or losing interest in what’s happening around them.
If you miss these early signs and your baby stays awake, they can become increasingly difficult to settle.
You might notice:
Crying or grizzling when you try to settle
Becoming increasingly frustrated
Difficulty calming
Fighting sleep
Taking a short nap and waking upset
Difficulty staying asleep
Suddenly appearing very alert or energised
An overtired baby doesn't necessarily look sleepy. Some babies become more irritable, restless, or hard to settle when they've stayed awake too long.
And sometimes, instead of looking sleepy, your baby can suddenly look like they’ve found a second wind.
They’re smiling.
They’re kicking.
They’re chatting.
They look completely awake.
Meanwhile, you’re thinking:
“But you’ve been awake for THREE HOURS. How are you still awake?!”
Yep. This is where baby sleep gets really confusing.
But What About an Undertired Baby?
An undertired baby simply hasn't built up enough sleep pressure yet to be ready for sleep.
This can happen when:
Their previous nap was particularly long
They’ve had more daytime sleep than usual
Their awake period was too short
Their sleep needs are beginning to change
They’re approaching a nap transition
You may notice that your baby is:
Happy and content in the cot
Chatting or playing instead of settling
Taking a long time to fall asleep
Resisting a nap without becoming particularly upset
Waking from a short nap relatively happy
Appearing alert and ready to keep going
An undertired baby may resist sleep simply because they haven't been awake long enough to build sufficient sleep pressure.
This is very different from a baby who is desperately trying to sleep but can't quite settle.
And this is why fighting sleep doesn't automatically mean your baby is overtired.
Sometimes they simply aren't ready yet.
The Biggest Clue? Look at Their Behaviour
This is where I encourage parents to become a little bit of a sleep detective.
Rather than asking:
“How long has my baby been awake?”
Also ask:
“What is my baby actually telling me?”
An overtired baby may become increasingly upset and difficult to settle, whereas an undertired baby may remain relatively happy, alert, and ready to keep going.
Think about:
What was their previous nap like?
How long have they been awake?
Are they happy and engaged?
Are they showing tired signs?
Are they becoming increasingly frustrated?
How long are they taking to settle?
The pattern is what matters.
What About Awake Windows?
Awake windows can be a really useful starting point. They can give you an idea of when your baby might be ready for their next sleep based on their age and developmental stage. But please don't feel like you have to put your baby to sleep at the exact minute. Babies aren't clocks.
One day your baby might be ready for sleep after a certain amount of awake time. Another day they might comfortably stay awake a little longer.
As babies grow, their sleep needs and the amount of time they can comfortably stay awake will change.
This is why I prefer using awake windows alongside your baby's individual cues, rather than treating them as a strict rule.
So How Do You Know Which One You're Dealing With?
Here's the simple version.
If your baby is overtired…
You may notice:
Increasing fussiness
Crying when you try to settle
Difficulty calming
Fighting sleep despite clearly being tired
Short or unsettled naps
A sudden burst of energy or alertness
Babies who become overtired can be harder to settle and may have difficulty getting the restorative sleep they need.
If your baby is undertired…
You may notice:
They're happy and alert
They're chatting or playing in the cot
They're taking a long time to fall asleep
They protest being put down but don't seem particularly upset
They wake from a short nap relatively happy
When there isn't enough sleep pressure, your baby may simply need a little more awake time before they're genuinely ready for their next sleep.
Of course, babies don't always read the textbook!
There will be days when your baby is overtired.
There will be days when they're undertired.
And there will absolutely be days when nothing seems to make sense.
Welcome to parenting!
What If Your Baby Is Overtired?
If you suspect your baby has become overtired, your goal isn't to create the perfect sleep environment or follow a complicated settling routine.
Your first job is to help them regulate and calm.
Reduce stimulation.
Dim the lights.
Slow everything down.
Use your usual calming techniques.
Cuddle them.
Rock them.
Pat them.
Feed them if they need a feed.
Do whatever responsive settling approach works for your baby and your family.
Reducing stimulation and creating a calmer environment can make it easier for an overtired baby to move towards sleep.
And if the day has completely gone off track?
That's okay.
One difficult nap does not ruin your baby's sleep.
What If Your Baby Is Undertired?
If your baby is happy, alert, and clearly not ready for sleep, you don't necessarily need to spend 45 minutes trying to convince them to sleep.
Sometimes they simply need a little more awake time.
Give them some calm play.
Interact with them.
Let them move their body.
Then try again when you start seeing those sleepy cues.
As babies grow, they can comfortably manage longer periods awake, which is one of the reasons sleep timing and nap needs change over time.
What worked beautifully a few months ago may suddenly stop working.
That doesn't mean you're doing anything wrong. It means your baby is developing.
What If Your Baby Is Fighting Sleep?
This is probably one of the most common questions I get.
“But Chloe, my baby is clearly tired... so why are they fighting sleep?”
And this is where we need to look beyond the word tired.
A baby can fight sleep because they are overtired.
They can also fight sleep because they're undertired.
They may be uncomfortable.
They may be hungry.
They may be overstimulated.
They may be going through a developmental change.
Or they may simply need a little more support to settle.
There are many possible reasons babies resist sleep, so fighting a nap or bedtime doesn't automatically tell us that they're overtired.
So rather than automatically assuming:
“They're fighting sleep, therefore they're overtired.”
I encourage you to step back and look at the bigger picture.
Become the sleep detective.
Don't Chase the Perfect Awake Window
This is probably one of my biggest pieces of advice.
Please don't spend your entire day watching the clock.
Sleep isn't a mathematical equation. Your baby might sleep beautifully after a particular awake period one day and completely refuse the same nap the next.
Instead, think of awake windows as a guide.
Then layer in:
Your baby's cues + their previous sleep + their age + their individual sleep needs.
That's where you start getting a much clearer picture.
And if you get it wrong? Adjust.
You don't have to overhaul your entire routine because one nap didn't work.
The Bottom Line
Your baby doesn't need you to get every sleep perfectly timed.
They need you to learn their cues, understand their individual needs, and respond to what they're communicating.
Sometimes they need more awake time.
Sometimes they need less.
And sometimes, despite doing everything “right”, your baby simply has a rubbish nap!
That's normal too.
Sleep isn't about perfection. It's about understanding, responding, and finding what works for your individual child.
If you're struggling to work out your baby's sleep needs or constantly wondering whether they're overtired, undertired, or simply having a tricky day, I can help.
At Sleep Again, I create personalised sleep plans that take into account your child's age, temperament, sleep needs, development, and your family's individual circumstances.
Because there is no one-size-fits-all approach to baby sleep.
Connection & consistency can absolutely work together.
