Four months is the most significant sleep milestone in the first year โ and often the most difficult. The 4-month sleep regression isn't a phase that passes. It's a permanent change in how your baby sleeps, and how you respond to it shapes sleep for months to come.
What Changes at 4 Months
Before 4 months, babies cycle primarily through light and deep sleep. At 4 months, their sleep architecture permanently matures to include the full adult cycle: light sleep โ deep sleep โ REM โ back to light sleep. This cycle takes 45โ50 minutes. At the end of each cycle, babies partially rouse. Previously they'd slip back under easily. Now they wake fully โ and if they need help to fall asleep (feeding, rocking), they'll need that help again at every cycle boundary.
Wake Windows at 4 Months
By 4 months, wake windows have stretched to 1.5โ2 hours. Many babies are moving toward a 4-nap schedule, though some are still on 5.
Sample Schedule
7:00 AM โ Wake, feed
8:30 AM โ Nap 1 (45โ60 min)
10:00 AM โ Wake, feed
11:30 AM โ Nap 2 (45โ60 min)
1:00 PM โ Wake, feed
2:30 PM โ Nap 3 (30โ45 min)
4:00 PM โ Wake, feed
5:15 PM โ Catnap (20โ30 min)
7:00 PM โ Bedtime routine begins
7:30 PM โ Bedtime
Night โ 1โ3 feeds still expected
The Most Important Thing You Can Do
Start practising drowsy but awake at every sleep. This means putting your baby down when they're sleepy but still conscious โ not fully asleep. It's the single most important habit to establish at this age. It's hard at first. It gets easier within 1โ2 weeks and pays off for months.