If you're reading this at 3am with a baby who was sleeping through the night and suddenly isn't, we want you to know two things: you're not doing anything wrong, and this doesn't last forever.
Sleep regressions can feel like a cruel joke, just when you get into a rhythm, it falls apart. But regressions aren't setbacks. They're signs that your baby's brain and body are doing exactly what they're supposed to be doing: growing, fast. Here's what's actually happening at each stage, and roughly how long it tends to last.
The 4-Month Regression
This is the big one, and honestly, it's less a "regression" and more a permanent shift. Around 4 months, your baby's sleep architecture matures, they move from newborn sleep cycles into the same light-and-deep sleep cycles adults have. That's a wonderful thing long-term, but it also means they wake more between cycles and need help settling back down.
What you'll notice: shorter naps, more night wakings, a baby who suddenly won't sleep unless held or fed to sleep.
How long it lasts: typically 2–6 weeks, though the underlying sleep changes are permanent, this is often when it helps to start gently building independent settling skills, since your baby's sleep is now "adult-like" for good.
The 6-Month Regression
Not every baby hits a dramatic regression at 6 months, but many go through a rough patch here tied to a growth spurt, the start of solid foods, or teething. Separation awareness is also beginning to show up, your baby is starting to notice when you leave the room.
What you'll notice: more frequent night wakings, fussiness around new foods or emerging teeth, needing more comfort to fall back asleep.
How long it lasts: usually 2–3 weeks. Consistency with your routine during this stretch tends to pay off quickly once the growth spurt or teething passes.
The 8-Month Regression
This one is closely tied to a developmental leap: crawling, pulling to stand, babbling, and a much stronger sense of object permanence. Your baby now understands that when you leave, you still exist which is exactly why bedtime separation can suddenly feel so much harder.
What you'll notice: bedtime protest, night wakings paired with practicing new physical skills (yes, some babies literally practice standing in their crib at 2am), increased clinginess.
How long it lasts: typically 2–4 weeks. Extra reassurance and a steady routine go a long way here, this phase responds well to predictability.
The 12-Month Regression
Right around the first birthday, walking (or almost-walking), a wave of new language, and often a nap transition from two naps to one all tend to collide. That's a lot of change at once, and sleep usually feels it first.
What you'll notice: early morning waking, resistance to the second nap, more emotional bedtimes.
How long it lasts: usually 2–4 weeks, though if the nap transition is part of what's going on, it may take a bit longer for the new one-nap rhythm to fully settle.
The Thread That Connects All of Them
Every regression on this list is temporary. Every single one is tied to real, healthy development, a brain that's learning, a body that's growing, a little person becoming more aware of the world and the people in it. That doesn't make the 3am wake-ups easier in the moment, but it does mean there's a light at the end of each one.
What helps most, across every stage, isn't a single trick; it's having a steady, responsive rhythm you can lean on when things get wobbly, and knowing enough about what's normal to tell the difference between "this is a phase" and "let's check in with the pediatrician."
That's the whole idea behind Rested: not a rigid formula, but support that meets you and your baby where you actually are, stage by stage, regression by regression, so you're never guessing alone at 3 am.
You're doing better than you think you are. This part passes.
