Why it happens
Sleep architecture matures around this age. Babies may wake more clearly between cycles and need help linking them.
What helps most
Protect naps as much as possible, keep bedtime calm and age-appropriate, and focus on one gentle sleep change at a time.
How long it lasts
It varies. Some babies move through it quickly, others need more time and support.
Important: baby sleep varies enormously. Avoid one-size-fits-all promises, and always prioritise feeding, growth and safe sleep advice.
Safer sleep reminder. For babies, use a firm, flat sleep surface and follow the latest safer sleep advice from the NHS and The Lullaby Trust.
Want to know what is disturbing your baby's sleep?
The Petit Nuage sleep quiz looks at age, naps, night waking and settling habits to show you what to focus on first.
Take the 2-minute quiz →Frequently asked questions
Is the 4 month regression real?
Yes, in the sense that sleep often changes around this stage.
Should I sleep train during it?
There is no need to rush. Start with timing and routines first.
Will it pass by itself?
Sometimes, but some patterns can persist without small adjustments.
Reference sources: NHS baby sleep guidance · The Lullaby Trust safer sleep information. Last updated: 24 September 2026.