The 8-10 month sleep regression: what's actually happening (and how long it lasts)
It's almost always the same call.
A baby who had been sleeping pretty well, somewhere around eight or nine months, has suddenly fallen apart. Multiple wakes a night, fighting bedtime, half the naps refused. The parent has tried earlier bedtime, later bedtime, capping naps, dropping the third nap entirely. Nothing has shifted things meaningfully and the assumption is that something has gone wrong.
Most of the time, nothing has gone wrong. There is a real developmental window between roughly 8 and 10 months (and really…all the time for the first two years) where three things tend to happen at once, and any one of them alone is enough to disrupt sleep. All three at the same time produces what looks like a regression but is actually a stack of normal shifts.
Why this window is its own thing
The four-month sleep changes get all the attention because that's when sleep architecture itself reorganises. The 8-10 month window is different. This time the underlying sleep biology isn't what's shifting. What you're seeing is a cluster of cognitive and physical developments landing close together, and these can interfere with sleep. It tends to look more behavioural than biological from the outside, which is why parents usually try to fix it with schedule changes that don't quite land.
The three things happening at once
The first is object permanence. Around this age, babies start to genuinely understand that you continue to exist when you leave the room. Before this, "out of sight" was closer to "doesn't exist right now". Once this realisation sets in, waking up at 2am and finding you absent is upsetting in a way it wasn't six weeks earlier. The same baby who could stir and resettle alone may now wake fully looking for you.
The second is the nap transition from three naps to two. The third nap usually starts becoming the one that's hardest to get and easiest to lose. As it drops, bedtime tends to move earlier, the second nap may need to lengthen, and the rhythm of the day looks different for a few weeks while everything resettles. During the transition, sleep can look chaotic. After it lands, things usually smooth out.
The third is physical movement. You can see many babies starting to crawl, some even start to walk (!?) in this window and that leads to their brain’s fizzing trying to practice overnight. Research suggests sleep can go a little wonky around big periods of development, but especially physical development, and so whilst annoying, it’s all part and parcel of them growing up.
How long it usually lasts
Most of the time, each singular issue can displace sleep for a few days up to a few weeks. Separation anxiety alongisde object permanence is more of a longer-term support and it will come and go in intensity over the next year or so. If all three things hit at once, I’d hold onto your hat for 2-4 weeks. Some families see it resolve faster, particularly if the nap transition lands cleanly and the rest of the day rebalances quickly. Some take closer to six weeks, but this isn’t a clean process, nor does it usually all hit at once.
You'll usually know it's resolving when wakeups start clustering rather than scattering across the night, when bedtime resistance relaxes again, and when the new two-nap rhythm starts to feel like the normal day.
What to do (and what not to do)
Do not, I repeat do not, immediately change everything, including their schedule at the first sign of a sleep wobble. The temptation is there, I get it. Especially if things have been smooth for a few weeks or months. But, try to just see what their new normal is at least over a few nights.
What to do: keep the wind-down consistent, hold the response patterns you'd usually use at this age, and be a little more patient with the bridge between fully awake and fully asleep. If you're going in to comfort, go in. Any sleep skills they had a month ago haven't been lost. They've been temporarily overrun by a developmental moment, and they come back.
I do usually look at dropping to 2 naps if you haven’t already. By this time, it can make a big difference in overnight sleep quality.
If it's been more than three weeks and things are still all over the place, that's usually a good time to look at what specifically isn't shifting. It may be as simple as extending the evening routine to spend more intentional time together so the separation at bedtime is easier.
A note on the timing of help
The hardest part of this window is that the parent is exhausted after two weeks of a sleep shift and starts second-guessing every part of the setup. It usually isn't the setup. It's the developmental moment running through it.
If you're in this and you'd like a closer look, our consultations were built for exactly this kind of moment: a baby who used to sleep, a parent who is now uncertain, a window that needs to be moved through rather than fixed.
What are you noticing most about your baby right now? I'd love to hear.