Sleep regressions: the 4-month change and the rest

Work it out for your family: Baby sleep schedule by age. Today's wake windows, naps and bedtime for your baby's age, and what changes next.

The short answer

The 4-month change is real. Around 3 to 4 months, your baby’s sleep matures. Some babies wake more for a few weeks while it settles. Others sail through [1][2].
8 to 10 months has some evidence. Crawling, pulling up and separation anxiety can bring more night waking for a while [3][4].
The 12-month and 18-month “regressions” are folk wisdom. No research shows them as distinct, predictable events [2][5].
Over the first two years, night wakings trend down on average, though not in a straight line [2]. A rough few weeks is common. A permanent step back is not.

“Sleep regression” isn’t a medical term. Search the medical literature for it and “you won’t find anything,” says Yale pediatric sleep physician Craig Canapari [5]. The word makes normal development sound like going backward. Most of what it describes is your baby growing up.

Safe sleep stays first

A rough patch is when tired adults bend the rules. Don’t. Whatever happens at 3 a.m. [6]:

Put your baby down on their back, every sleep, until the first birthday.
Use their own crib, bassinet or play yard, firm and flat, with only a fitted sheet.
Share a room, not a bed. The AAP can’t support bed-sharing under any circumstances.
If you might doze off while feeding, don’t feed on a couch or armchair. If you fall asleep, move your baby to their own space as soon as you wake.

The full list is in our safe sleep guide.

The 4-month change

This is the one with real science behind it.

The body clock switches on. A day-night rhythm starts to emerge at around 10 to 12 weeks [2].
Sleep cycles mature. The American Academy of Pediatrics (AAP) says babies don’t have regular sleep cycles until about 4 months [1].

As sleep becomes more adult-like, some babies surface between cycles and need help settling again. That can look like a baby who “forgot” how to sleep.

What the research doesn’t show is a population-wide dip. A review of infant sleep studies pooled the data: night wakings averaged 1.7 a night at 0 to 2 months and 0.8 at 3 to 6 months [2]. Your baby may wake more for a while. Babies on average don’t.

8 to 10 months: on the move

Two things collide here.

New motor skills. In one study of 8-month-olds, those who had started crawling had more broken sleep than those who hadn’t [3]. A later study followed 28 babies from 5 to 11 months and found a rise in night waking around the start of crawling. The researchers reported that sleep generally went back to its earlier pattern within about 3 months [7].
Separation anxiety. From the second half of the first year, it can cause many nights of disrupted sleep. Your baby may wake and cry for you, often for one parent in particular. It usually fades around the second birthday [4].

Pooled data hint at this too: night wakings averaged 1.1 a night at 7 to 11 months, up from 0.8 at 3 to 6 months [2]. Those figures come from different studies, so treat them as a hint, not proof. The evidence is real but small. A fixed “8-month regression” date is a folk label [3][5].

12 and 18 months: labels, not events

No research supports a distinct 12-month or 18-month regression [2][5]. Pooled data put night wakings at about 0.7 a night on average between 1 and 2 years, the lowest of any band in the first two years [2].

What’s real at these ages:

Around 12 to 15 months, learning to walk can bring a patch of night waking. It tends to settle once the skill is mastered [5].
Somewhere in the second year, most toddlers go from 2 naps to 1. Pooled data average about 1.2 naps a day at 1 to 2 years [2]. Canapari says toddlers usually drop the morning nap between 18 and 24 months [5]. Nearly all still nap: in a long-running Swiss study, 96% of 18-month-olds did [8].
Around 18 months, separation anxiety can still be strong. It usually fades around the second birthday [4].

Other things that look like a regression

Nap changes. Babies usually drop from 3 naps to 2 somewhere between about 6 and 15 months [5]. Research puts the average at about 2 naps a day at 6 to 11 months, with wide variation [2].
Teething. First teeth usually come between 6 and 10 months, and sore gums can make babies fussy. A fever isn’t a teething sign. If your baby has one, look for another cause and call your pediatrician [9].
Time changes. Most children adjust within a week or two [10].

What helps

Families choose different approaches to sleep, and this guide doesn’t push a method. These are the AAP’s general tips [1]:

Keep nights calm and quiet. Feed and change your baby without much talk or light.
Make days for play. Talking, reading and playing during the day helps longer sleep at night.
From about 4 months, the AAP suggests putting your baby down drowsy but awake, so they learn to fall asleep in their own bed.
Waking is normal. The AAP notes it’s normal for a 6-month-old to wake and resettle after a few minutes. You can still feed, change or comfort them when they need it.

For separation anxiety, the AAP recommends a loving, consistent approach. Your child may need reassurance several times a night until it passes [4].

If you’re weighing a structured sleep-training method, one Australian trial is worth knowing. It offered behavioral sleep techniques at 8 to 10 months to families who’d reported a sleep problem, then followed them to age 6. It found no lasting harms and no lasting benefits, either way [11]. That’s evidence for choosing what fits your family, not for any one method.

When to call your pediatrician

Under 3 months with a temperature of 100.4°F (38°C) or higher: call right away [12].
Snoring often, or trouble breathing in sleep: tell your pediatrician [13].
Breathing that stops for more than 20 seconds: call 911 [13].
Still unsettled more than a week or two after a time change [10], or sleep that’s wearing down the whole family: ask.
You’re exhausted or low. If you worry you’ll fall asleep holding your baby, or think you might have postpartum depression, talk to your doctor. The National Maternal Mental Health Hotline is 1-833-TLC-MAMA (1-833-852-6262). In a crisis, call or text 988 [14].

Sources

HealthyChildren.org (AAP), “Getting Your Baby to Sleep.” healthychildren.org
Galland BC, et al., “Normal sleep patterns in infants and children: a systematic review of observational studies,” Sleep Medicine Reviews 2012;16(3):213–222. doi.org
Scher A, “Crawling in and out of sleep,” Infant and Child Development 2005;14(5):491–500. doi.org
HealthyChildren.org (AAP), “Separation Anxiety & Sleeping Trouble in Young Children.” healthychildren.org
Canapari C, “A Comprehensive Guide to Sleep Regressions” (Yale pediatric sleep physician; November 2025, updated May 2026). drcraigcanapari.com
HealthyChildren.org (AAP), “How to Keep Your Sleeping Baby Safe: AAP Policy Explained.” healthychildren.org
Scher A, Cohen D, “Sleep as a mirror of developmental transitions in infancy: the case of crawling,” Monographs of the Society for Research in Child Development 2015;80(1):70–88. doi.org The 3-month figure is from the University of Haifa’s report of the study. news-medical.net
Iglowstein I, et al., “Sleep duration from infancy to adolescence: reference values and generational trends,” Pediatrics 2003;111(2):302–307. doi.org
HealthyChildren.org (AAP), “Teething Pain.” healthychildren.org
Children’s Hospital of Philadelphia, “5 ways to help kids adjust to daylight saving time.” chop.edu
Price AMH, et al., “Five-year follow-up of harms and benefits of behavioral infant sleep intervention: randomized trial,” Pediatrics 2012;130(4):643–651. doi.org
HealthyChildren.org (AAP), “Fever: When to Call the Pediatrician.” healthychildren.org
HealthyChildren.org (AAP), “Sleep Apnea in Children: Detection & Treatment.” healthychildren.org
Health Resources and Services Administration (HRSA), “National Maternal Mental Health Hotline.” mchb.hrsa.gov, and 988 Suicide & Crisis Lifeline. 988lifeline.org

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