Published by Actually Sleeping · Reviewed by Dr. Samantha Abrahamson, PharmD · Review policy · Updated 2026-11-10

How do a baby’s sleep cycles and circadian rhythm develop?

Newborns have no day–night rhythm yet and sleep in short cycles spread around the clock. Over the first months the body clock develops, a nightly melatonin rhythm appears, and sleep consolidates toward night. Every cycle ends in a brief partial waking, which is why a baby who needs feeding or rocking to fall asleep often wakes and asks for it again through the night.

A note on scope: Dr. Sam is a Doctor of Pharmacy and a licensed pharmacist, not your baby’s physician. This guide explains how a medication relates to sleep. Whether and how your child takes any medication is a decision for your pediatrician.

What changes in the first months

Short cycles. An infant’s full cycle of non-REM and REM sleep lasts about 50 minutes, compared with about 90 minutes in adults. A brief partial waking between cycles is normal at every age.
Active sleep first. Newborns fall asleep through active sleep, the newborn version of REM, which is one reason they rouse so easily.
The body clock arrives. The roughly 24-hour circadian rhythm develops over the first months, and with it a nightly melatonin rise. That is when the longest stretch of sleep starts to land at night.
Total sleep need. The American Academy of Sleep Medicine recommends 12–16 hours per 24 hours at 4–12 months and 11–14 hours at 1–2 years, naps included, and makes no recommendation under 4 months because normal sleep varies so widely.

Families often first contact Actually Sleeping when this maturing shows up as the “4-month regression.” It is not a phase to wait out. It is the point at which the way a baby falls asleep starts to matter at every cycle, and that is exactly what a plan written for your baby addresses.

Why this matters for night waking

Every baby surfaces briefly between cycles. The difference between a baby who sleeps through and one who wakes four times is what happens in that moment. A baby who fell asleep on their own can drift back. A baby who fell asleep feeding or rocking calls for the same thing again. The maturing of sleep in the first months does not create the problem; it reveals it.

Why general advice so often misses

Sleep biology is the same for every baby. What sits on top of it is not: feeding needs, temperament, how long a habit has existed, reflux or prematurity, siblings, work schedules. A tip that suits one baby can make another baby’s nights worse. That is why most families who come to Actually Sleeping have already tried things on their own.

What Actually Sleeping does about it

Dr. Sam writes a plan for your baby’s age, feeds, temperament and current way of falling asleep. You get bootcamp-style coaching before the first night, daily 1:1 check-ins and naps coached until solid. It is not cry it out and not wait it out, and the plan never asks you to drop night feeds; feeding decisions stay with your pediatrician. Parents who started around the 4-month change describe it in the 4-month regression video reviews.

Book the free consultation to talk through what your baby’s nights look like now.

Want this fixed for your baby?

Actually Sleeping is 1:1 coaching: a sleep plan written for your baby by Dr. Sam, bootcamp-style coaching before the first night, and daily check-ins until it is working. 700+ families coached, 129 video reviews, and a written guarantee: 8–12 hours through the night within 14 days, or a full refund.

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Frequently asked

When do babies start producing melatonin?

A day–night melatonin rhythm develops over the first months of life, alongside the body clock. Melatonin supplements do not speed this up, and the AAP says to use them only after talking with your pediatrician.

Why does my baby wake so regularly through the night?

Each waking often lines up with the end of a sleep cycle. The waking itself is normal; the crying is a request for whatever helped your baby fall asleep at bedtime. Changing that is what a custom sleep plan does.

How much sleep does a baby need?

AASM consensus: infants 4–12 months, 12–16 hours per 24 hours including naps; toddlers 1–2 years, 11–14 hours; children 3–5 years, 10–13 hours. The AASM makes no recommendation under 4 months.