A baby who was sleeping through the night suddenly starts waking every two hours, or a nap that used to be predictable cuts short at 20 minutes for days in a row. Before assuming something broke, it's worth checking the calendar: there's likely an age where that lines up with an expected developmental leap.
What a sleep regression is (and isn't)
A sleep regression is a period — typically 2 to 6 weeks — where a baby who had a fairly settled pattern starts waking more often, taking shorter naps, or struggling to fall asleep. It's not an actual setback or something to "fix": it usually lines up with a developmental leap (motor, cognitive, or language) that's literally reorganizing your baby's brain, sleep included.
The ages below are approximate, not a fixed calendar. Every baby reaches their milestones on their own timeline, so it's perfectly normal for "the 8-month regression" to show up at 7, 10, or 13 months.
Sleep regression chart by age
| Approximate age | What triggers it |
|---|---|
| 4 months | The most documented one — a permanent shift in sleep architecture, not something that just "passes." Baby moves to adult-like sleep cycles, with more brief wake-ups between cycles. |
| 6 weeks | Less talked about but real: lines up with an early cognitive leap and heightened sensory alertness. |
| 6 months | Often coincides with starting solids and shifts in nighttime appetite. |
| 8 months | The most noticeable motor leap of the first year kicks off — crawling or scooting starts, and that alone disrupts sleep. |
| 9 months | Sits up unassisted and starts pulling to stand at the crib rail — practicing the new skill even half-asleep. |
| 10 months | Faster crawling and first attempts at cruising along furniture — still part of the same motor leap. |
| 11 months | Close to walking solo, with separation anxiety starting to show up more at bedtime. |
| 12 months | Walking (or close to it) and weaning or a formula/milk switch often overlap in this window. |
| 13-14 months | First loose words and growing motor independence — more pronounced separation anxiety at bedtime. |
| 15 months | Language explosion in progress — understands far more than they can say, which can mean frustration right before sleep. |
| 16-17 months | Often overlaps with the first active boundary-testing at bedtime, not just passive anxiety. |
| 18 months | Usually comes with nap resistance and the first bedtime "boundary testing." |
| 2 years | The crib-to-bed transition, on top of more active imagination (nighttime fears) and, often, a new sibling arriving. |
How to tell it's a regression and not something else
Three signs help tell it apart from a routine or health issue:
- It shows up suddenly — the pattern shifts within a few days, not gradually.
- It lines up with something new — a tooth, a motor skill, more words: there's a visible "leap" happening in another area besides sleep.
- It has an expiration date — it improves on its own within 2 to 6 weeks, without needing to overhaul the whole routine.
If more than 6 weeks pass with no improvement, or your baby shows other symptoms (fever, discomfort, changes in daytime appetite), it's worth checking with your pediatrician instead of waiting for it to "pass on its own."
Full daily timeline — a real screen from the Alfonso app.
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Frequently asked questions
How long does a sleep regression last?
Generally 2 to 6 weeks. Beyond that, it's worth checking with your pediatrician.
Why is my baby having the 8-month regression at 10 months?
Because the ages are approximate — tied to the developmental leap, which each baby reaches on their own timeline, not a fixed calendar.
Does every baby go through every regression?
Not necessarily, or with the same intensity. Both are normal.
Keep reading
ℹ️ This article is informational and doesn't replace a pediatrician's judgment. If sleep changes drag on or come with other symptoms, always check with a healthcare professional.