What Is the 4-Month Sleep Regression and How Long Does It Last?

The 4-month sleep regression is a permanent neurological change, not a temporary phase — your baby’s sleep architecture matures into adult-like cycles and doesn’t go back. The disrupted period typically lasts two to six weeks, but sleep only returns to normal if your baby learns to fall asleep independently.

That last part is why waiting it out often doesn’t work here.

What actually changes: newborns drop straight into deep sleep and stay there. Around 3 to 5 months, babies start cycling through light and deep stages every 45 to 60 minutes, with brief arousals in between. This is a healthy, expected milestone. It just means every one of those arousals is now an opportunity to fully wake up.

Signs you’re in it: a baby who was sleeping 5 to 6 hour stretches is suddenly up every 1 to 2 hours. Naps collapse to 30 minutes. Bedtime becomes a fight. Appetite changes. Your baby seems more alert and more distractible during the day.

What helps. Start putting your baby down awake at bedtime, even if you’re still helping a lot. You don’t have to do formal sleep training at 4 months — you’re just building the skill.

Move bedtime earlier, often to 6:30 or 7pm. Overtiredness makes everything about this worse.

Make the room fully dark and run white noise all night.

Watch wake windows closely. At 4 months most babies max out around 1.5 to 2 hours.

And keep the feeds. Genuine hunger increases around this age. This is not the moment to night wean.

What doesn’t help: adding cereal to bottles, introducing brand-new sleep props you’ll have to remove later, or switching methods every three days.

If your baby is over 4 months and this has been going on more than six weeks, it isn’t the regression anymore — it’s a habit that’s set, and it responds well to a real plan.