Baby sleep regression calculator Practical, science-based guidance — no fluff.
4-month regression (the big one)
The only permanent regression — baby’s sleep cycles mature to adult-like 4-stage cycles. They now wake briefly between every cycle. Lasts 2–6 weeks. This is the right window to teach independent sleep skills.
8–10 month regression
Triggered by crawling, separation anxiety, and teething. Naps may shorten or shift. Lasts 2–6 weeks. Keep routine rock-solid.
12-month regression
Walking milestone + early nap transition attempt (most babies still need 2 naps until ~15 months). 1–3 weeks. Do not drop to 1 nap yet.
18-month regression
Molars, language explosion, and a push for independence. Bedtime resistance and night waking common.
2-year regression
New fears, vivid dreams, and big developmental leaps. A nightlight and a comfort object (now age-appropriate) can help.
Survival rules
- Hold the line on routine
- Offer comfort but don’t create new sleep associations you’ll need to undo
- Track wake windows with our calculator
- It always ends. Always.