The 4 month sleep regression: what's really going on
Your baby was sleeping in lovely long stretches. Then, somewhere around three or four months, it all fell apart. Now they're waking every hour or two, naps have shrunk to 30 minutes, and you're wondering what on earth you did wrong.
You didn't do anything wrong.
The short answer: the 4 month sleep regression is a permanent change in the way your baby sleeps. Their sleep matures into cycles, a lot more like ours, with lighter moments in between. Babies who need help to fall asleep often need the same help each time they surface between cycles. That's why the wake-ups multiply.
The one true sleep regression
You'll see plenty of posts about 8 month, 12 month, 18 month and 2 year sleep regressions. There's no evidence that sleep goes backwards at set ages like that. Sleep can wobble around new skills like crawling, standing or walking, but every little one reaches those at different times. The 4 month change is different. It's the only true regression, and it's a permanent change in how your baby's sleep works. It's also a sign their brain is developing exactly as it should.
In the early weeks, newborns drop into deep sleep quickly and stay there. From around three to four months, their sleep starts to cycle through lighter and deeper stages, much like an adult's. At the end of each cycle, they come up into lighter sleep, and sometimes fully wake.
We do this too. We just roll over, pull the duvet up and go back to sleep without remembering it. Your baby is still learning how to do that.
Signs of the 4 month sleep regression
Waking much more often at night, sometimes every 45 minutes to 2 hours
Short naps, often around 30 to 45 minutes (one sleep cycle)
Harder to settle at bedtime
Fussier, more distracted feeding in the day
New skills, like rolling, practised at every opportunity (including 2am)
It doesn't always happen at exactly four months. Some babies go through it a few weeks earlier or later.
How long does the 4 month sleep regression last?
The change in how your baby sleeps is permanent. But the rough patch usually eases within a few weeks, as your baby gets used to linking their sleep cycles.
If you're six weeks in and nothing's shifting, it's usually not the regression any more. It's become a pattern, and patterns can be changed.
What helps
Keep a consistent bedtime routine. The same few steps every night, in the same order, tell your baby what's coming. It doesn't need to be long. Bath, milk, sleeping bag, story and a cuddle is plenty.
Make the room work for sleep. Dark for night-time and naps, a comfortable temperature, and white noise if it helps your family.
Get in good daytime feeds. At this age babies are suddenly very interested in the world, and daytime feeds can get short and distracted. A quieter room for feeds can help, so they don't make up for it overnight.
Practise settling, some of the time. You don't have to change everything at once. Try putting your baby down drowsy or awake for one sleep a day, often bedtime, when sleep pressure is highest. See what they can do with a bit less help.
Follow your baby, not a chart. You might see advice telling you to keep your baby awake for an exact number of minutes. Every little one is individual, with their own natural rhythm and their own 24-hour sleep needs. Watching your baby, and looking at their sleep across the full day and night, will tell you far more than a chart will. A simple sleep log makes this much easier. I built Littles Baby Tracker so parents can see their baby's sleep across the whole day and night at a glance.
A safety note on rolling
Rolling often arrives around the same time. If you swaddle, The Lullaby Trust advises you stop swaddling with arms inside as soon as your baby shows signs of rolling. A baby sleeping bag is a good next step. Always put your baby down on their back to sleep.
When to talk to someone
If your baby seems unwell, is feeding much less than usual, or you're worried about their weight, speak to your GP or health visitor. Some sleep changes have a medical cause, and that should always be ruled out first.
And if you're just exhausted and the weeks are stacking up, please don't wait it out alone.
Frequently asked questions
What age is the 4 month sleep regression?
Usually between about 3 and 5 months, but every baby is different.
Does the 4 month sleep regression affect naps?
Yes, often. Many babies start waking after one sleep cycle, around 30 to 45 minutes.
Are there other sleep regressions after 4 months?
Not at set ages. Sleep can wobble when your little one is learning something new, like crawling, standing or walking, or going through separation anxiety. But those happen at different ages for every child, so there's no "8 month" or "18 month" regression to brace yourself for.
Should I start sleep training at 4 months?
There's no need to rush into anything. Small changes, like practising settling at bedtime, can make a big difference. When you're ready for more, a plan built around your baby's temperament and your parenting style will always work better than a one-size-fits-all method.
Want some help?
I work with families across the UK to get sleep back on track in a way that suits your baby and your family. No cry it out, no rigid schedules. See how my sleep support works, or book a free 15-minute sleep chat.
Becca x
