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What ages are common for sleep regressions in babies?

There's no single official list of 'regression ages,' but parents most often notice rockier sleep around 4 months, 6-9 months, and 12-18 months, linked to normal brain, motor, and attachment development.

Pediatric sources describe these as expected shifts toward more mature sleep, not a problem to fix, occurring gradually over the first several years.

Strength of evidence

Mixed

Guideline sources describe general developmental timing of sleep changes, but the specific term 'sleep regression' and its exact ages are not formally studied; supporting data come from observational cohort studies, not trials of 'regressions' themselves.

What the evidence says

Pediatric organizations don't actually use the term 'sleep regression' as a medical diagnosis. Instead, they describe normal, brain-driven changes in sleep patterns that happen as babies grow, learn new skills, and develop feelings like separation anxiety. These shifts can make a baby who was sleeping well suddenly wake more often or resist naps.

Commonly reported bumpy periods include around 4 months (when sleep cycles start maturing), 6 to 9 months (tied to more mature sleep architecture and the start of separation anxiety), and 12 to 18 months (as toddlers become more mobile and independent, and separation anxiety often peaks again). Some babies show noticeable object permanence and clinginess as early as 4 to 5 months, with more obvious separation anxiety by about 9 months, and many toddlers have another wave of separation-related sleep trouble at 15 to 18 months.

Research following infants over their first year found that sleep patterns shift in clear stages, with a noticeable split around 6 months between babies who self-settle well and those who still need more help, and further changes by 9 and 12 months. This supports the idea that certain ages are more likely turning points, even though 'regression' isn't the most accurate word for what's happening.

Because every baby's timeline differs, these ages are common patterns rather than fixed rules, and a pediatrician can help if sleep disruption is severe or prolonged.

Sources

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked July 28, 2026

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