Sleep regressions commonly happen at 4 months, 6 months, 8 to 10 months, 12 months, and 18 months, with some children experiencing another round around age 2. Not every baby hits every one of these windows, and some sail through ages that derail other families entirely. But these are the points where developmental changes are most likely to disrupt sleep, and each one has a different trigger.
The 4-Month Sleep Regression
The 4-month regression is the big one, and it’s the only regression rooted in a permanent biological change. Around this age, babies shift from newborn sleep patterns into more adult-like sleep stages. Instead of cycling between just two phases of sleep, they begin moving through multiple stages, strung together in cycles lasting 60 to 120 minutes at night.
At the end of each cycle, your baby briefly surfaces into a light stage of sleep. During these partial awakenings, they check in with their surroundings. If something has changed since they fell asleep (you were holding them, the room was brighter, a pacifier was in their mouth), they’re more likely to wake up fully and cry. This is why a baby who slept beautifully as a newborn can suddenly start waking every one to two hours. The sleep architecture itself has matured, and it doesn’t revert back.
The 6-Month Regression
Around 6 months, separation anxiety starts to emerge. Your baby is beginning to understand that you exist even when you leave the room, but they haven’t yet grasped that you’ll come back. This new awareness can make bedtime and middle-of-the-night wakings more emotionally charged. Not all babies go through a noticeable regression at this age, but for those who do, the tearful resistance at being put down is the hallmark sign.
The 8- to 10-Month Regression
This window is packed with physical milestones. Babies at this age are often learning to sit up, crawl, pull themselves to standing, babble, and stack objects. Their brains are busy, and that busyness doesn’t shut off at night. It’s common to find an 8- or 9-month-old standing in their crib at 2 a.m., practicing a skill they picked up that afternoon.
Object permanence also solidifies during this stretch. Your baby now fully understands that things (and people) still exist when they can’t see them. That’s a cognitive leap, but it also fuels a surge of separation anxiety. The combination of physical restlessness and emotional clinginess makes the 8-to-10-month period one of the most disruptive regression windows for many families.
The 12-Month Regression
By their first birthday, children tend to show greater emotional engagement, increased communication, and expanded physical abilities like standing and walking with support. All of that stimulation can spill over into sleep. Separation anxiety often intensifies further at this age, and some children are also dealing with teething discomfort from molars starting to push through.
Many families are also adjusting nap schedules around 12 months, transitioning from two naps to one. That shift alone can temporarily throw off nighttime sleep, making it hard to tell whether your child is in a true regression or just adapting to a new daytime routine. Often it’s both at once.
The 18-Month Regression
The 18-month regression is notorious because toddlers now have the physical ability and the willpower to resist bedtime in ways a younger baby can’t. They can climb, run, and vocalize their opinions. An increased sense of independence means they may flat-out refuse to lie down, and the expanded mobility makes it harder to keep them in one place.
Emotionally, toddlers at this age are developing deeper reactions. Separation anxiety can resurface or worsen. Cognitive growth is rapid, with thinking, reasoning, and language skills all expanding considerably. Nightmares are possible at this age, though still uncommon. Teething from canines or second molars may also play a role. The combination of all these factors tends to make the 18-month regression feel especially stubborn.
The 2-Year Regression
Sleep regression is especially common in toddlers, and the period around age 2 is sometimes called the 2-year-old sleep regression. Triggers at this stage tend to be situational on top of developmental: potty training, transitioning from a crib to a bed, the birth of a new sibling, or a move to a new house. Any major life change layered onto the normal cognitive and language explosions of toddlerhood can temporarily derail sleep.
How Long Regressions Last
Most sleep regressions last two to four weeks. The 4-month regression can feel longer because the underlying change to sleep architecture is permanent, meaning your baby won’t go back to sleeping the way they did as a newborn. But the acute disruption, the frequent night wakings and short naps, typically settles within that same two-to-four-week window once your baby adjusts to their new sleep cycles.
Regression vs. Teething or Illness
Sleep regressions show up as a sudden, significant decline in sleep patterns: more night wakings, difficulty settling, increased crying at sleep times, and short or skipped naps. The key word is sudden. If your baby was sleeping reasonably well and then wasn’t, a regression is a likely explanation when the timing lines up with a developmental leap.
Teething can look similar at night, but it leaves clues during the day too. A teething baby tends to be uncomfortable during waking hours, with swollen or tender gums, increased drooling, biting and chewing on objects, and sometimes refusal to eat. If the sleep disruption only shows up at sleep times and your child seems fine during the day, development is the more likely culprit.
Illness is usually the easiest to distinguish. A fever over 100.4°F, diarrhea, or vomiting are not caused by teething or regressions and warrant a call to your pediatrician.
What Helps During a Regression
The single most useful thing you can do is keep your routines consistent. Do the same things in the same order at naptime and bedtime. A predictable sequence (bath, book, feeding, crib) gives your baby cues that sleep is coming, even when their internal wiring is in flux. Make sure both caregivers can run the same routine so it doesn’t depend on one person.
During nighttime wakings, keep the environment boring. Lights stay dim, voices stay low, and interactions stay brief. The goal is to signal that the middle of the night is not playtime. When your baby cries, try a graduated response: look at them first, then use your voice softly, then progress to light touch or gentle rocking. Give a pause between each step. This approach helps your baby start learning to settle without immediately escalating to being picked up.
Putting your baby down drowsy but still slightly awake is one of the more effective long-term strategies. It teaches them to bridge the gap between wakefulness and sleep on their own, which becomes especially important after the 4-month regression when they’re waking briefly between every sleep cycle.
If you’re exhausted, accept help. A partner, family member, or trusted friend taking one night shift or a block of daytime hours can make a real difference in your ability to stay patient and keep sleep practices safe. Avoid feeding your baby on a couch or armchair when you’re very tired, since falling asleep in those positions carries a suffocation risk. If you do doze off during a feeding, move your baby to their crib on their back as soon as you wake.