What is the 4-month sleep regression?

What's actually happening

Newborns drop straight into deep sleep and spend most of their sleep there. Around 3–5 months, that architecture permanently matures into the adult pattern: cycles of roughly 45–60 minutes moving through light and deep stages, with brief natural wakings between cycles. A baby who needs feeding, rocking or a dummy to fall asleep will often call for that same help at every cycle boundary — which is why the waking suddenly multiplies.

Why "regression" is the wrong word

Nothing has gone backwards — this is a one-way upgrade to mature sleep. That also means it doesn't simply "pass" like a growth spurt: the new cycles are permanent, and what changes is your baby learning to link them.

What helps

• A consistent, boring wind-down at every bedtime, so sleep cues do some of the work.
• Full feeds in daylight hours to gently shift calories away from the night.
• Practising cot-settling — drowsy-but-awake some of the time, without turning it into a battle.
• Holding your safer-sleep line: back to sleep, clear cot, room-share to 6 months, whatever the night throws at you. Our sleep training methods comparison covers the structured options if you choose that route later.