Sources & methodology

Primary sources

• American Academy of Pediatrics — HealthyChildren.org sleep section: infant sleep development, safe sleep, and age-by-age expectations.
• NHS (UK) — baby sleep guidance: practical settling guidance and normal infant sleep patterns.
• Cleveland Clinic — sleep regression overview: definitions, common ages and typical duration.
• CDC / WHO growth and development materials — developmental milestone timing that underpins the "why" behind each regression window.

How we use them

• Age windows. The ranges in our chart and calculator (e.g. the 4-month regression spanning roughly 3–5 months) reflect the commonly reported windows across these sources. Where sources differ, we use the wider range and say "around."
• Durations. The two-to-six-week typical duration is the consistently reported range; we note where a stage tends to run shorter.
• Recommendations. Routine consistency, age-appropriate wake windows, daytime skill practice and responsive comfort are the through-lines of mainstream pediatric sleep guidance. We do not invent techniques, and we do not recommend anything that conflicts with AAP safe-sleep guidance.

What we deliberately don't do

• No medical advice, diagnosis, or medication guidance — those questions belong to your pediatrician.
• No invented statistics. If a number appears on this site, it comes from a cited source or is clearly framed as a typical reported range.
• No fear marketing. Regressions are normal development, and our job is to make them less scary, not more.

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