Sleep Regression Calculator & Timeline

How this sleep regression calculator works

Enter your baby's birth date above and the calculator maps the six most commonly reported sleep disruption windows: around 4 months, 6 months, 8 to 10 months, 12 months, 18 months, and 2 years. Each window gets real dates computed from her birthday, plus a status: passed, likely now, or ahead.

One honest caveat: these windows are commonly reported, not universal. Think of the result as a weather map, not a train schedule. A stormy stretch at this age is normal, not something you caused.

Sleep regression ages: the windows on the timeline

Here is the sleep regression timeline most families recognize.

Around 4 months (roughly 3.5 to 5 months). The big one. Sleep cycles mature into an adult-like structure, a lasting change, so babies who slept long stretches may suddenly wake between cycles.
Around 6 months. Rolling both ways, early sitting, babbling, and a growing fascination with the world.
8 to 10 months. Often called the 8 month sleep regression. Crawling, pulling up to stand, and a first wave of separation anxiety tend to arrive together.
Around 12 months. First steps and first words are close, and some babies briefly protest naps around their first birthday.
Around 18 months. The 18 month sleep regression tends to come with a language surge, new independence, and separation anxiety making a comeback.
Around 2 years. A bigger imagination, sometimes new fears of the dark, and a genuinely lower total sleep need.

Sleep regressions chart: every window at a glance

Ready to screenshot for your partner at 6am.

Age window	What is changing	How long it commonly lasts
Around 4 months (3.5 to 5 months)	Sleep cycles mature into an adult-like structure with more light sleep stages, a lasting change in how your baby sleeps	2 to 6 weeks for the rocky patch; the new sleep structure is permanent
Around 6 months	Rolling both ways, early sitting, babbling, growing awareness of the world	Typically 2 to 6 weeks
8 to 10 months	Crawling, pulling up to stand, and a first wave of separation anxiety	Typically 2 to 6 weeks
Around 12 months	First steps, first words, sometimes a short nap strike	Often shorter, up to a few weeks
Around 18 months	Language surge, new independence, separation anxiety returning	Typically 2 to 6 weeks
Around 2 years	Bigger imagination, new fears, bedtime resistance, lower total sleep need	Typically 2 to 6 weeks

Why the 4 month sleep regression gets its own reputation

Every other window is tied to a passing burst of development. The 4 month change is structural: somewhere between about 13 and 20 weeks, your baby's brain reorganizes how it cycles through sleep, adding lighter stages where she can fully wake between cycles.

Nothing is wrong; her sleep simply works differently now. Practicing falling asleep at bedtime often helps, because the skill she uses at 7pm is the same one she needs at 2am.

How long do sleep regressions last, and what helps

Most regressions ease within 2 to 6 weeks; some pass in days. While you are in one, the boring advice is the good advice:

Keep the routine steady. A predictable wind-down (bath, feed, book, song) is an anchor when everything else feels chaotic.
Give practice, gently. Where it feels right, give your baby chances to settle herself at bedtime.
Watch wake windows. An overtired baby fights sleep harder; slightly earlier bedtimes often help.
Comfort freely, commit carefully. Extra soothing is kind; whatever you repeat nightly may become the expectation.
Protect your own sleep. Tag-team nights where you can and lower the bar on everything else. You matter too.

Is it a regression or something else?

Regressions are annoying but well: a baby in one is generally her usual self during the day, feeding, playing, and gaining weight, just sleeping worse. Call your pediatrician if you notice any of these:

Fever, especially 100.4 F (38 C) or higher in a baby under 3 months, or any fever that worries you
Pulling or rubbing an ear, particularly with crying or after a cold (a common sign of an ear infection)
Any change in breathing: fast, labored, noisy, or pauses
Refusing several feeds in a row, or noticeably fewer wet diapers
Crying that cannot be consoled, or unusual lethargy and floppiness
Sleep that keeps getting worse for more than six weeks with no good nights in between

You know your baby better than any chart does. If your gut says something is off, call.

Sources and method: this tool adds each commonly reported window (3.5 to 5 months, around 6 months, 8 to 10 months, around 12 months, around 18 months, and around 2 years) to the birth date you enter, then compares today's date against each range to mark it passed, likely now, or ahead. Window ages and the typical 2 to 6 week duration are drawn from the Sleep Foundation and Cleveland Clinic; guidance on illness signs such as ear infections comes from the American Academy of Pediatrics via HealthyChildren.org.

Frequently asked questions

What ages do sleep regressions happen?

Sleep disruptions are most commonly reported around 4 months, 6 months, 8 to 10 months, 12 months, 18 months, and 2 years. Not every baby hits every window, and timing can shift by a few weeks in either direction.

How long does the 4 month sleep regression last?

The rocky stretch typically lasts 2 to 6 weeks, though the underlying change to your baby's sleep cycles is permanent. Once she learns to link the new sleep cycles together, nights usually settle again. Steady routines and practice falling asleep independently can shorten the bumpy period.

Is there an 8 month sleep regression or a 9 month sleep regression?

They are the same thing. Most sources describe one broad window that can open anywhere from 8 to 10 months, so some parents call it the 8 month sleep regression and others the 9 or 10 month regression. It usually lines up with crawling, pulling up, and separation anxiety.

How do I know if it is a sleep regression or teething?

A regression usually arrives alongside a new skill and improves within a few weeks, while teething discomfort tends to be shorter and often comes with drooling, gum rubbing, and chewing on everything. Fever of 100.4 F (38 C) or higher, ear pulling with crying, or refusing feeds are not typical of either one, so check with your pediatrician if you see those signs.

Do all babies go through sleep regressions?

No. These windows are common but not universal. Some babies sail through every one without a bad night, others struggle in two or three, and a few hit rough patches at unscheduled moments. The 4 month change in sleep cycle structure happens to every baby, but how visibly it disrupts sleep varies.

What is the 18 month sleep regression?

A commonly reported stretch of disrupted sleep around 17 to 19 months, often linked to a language surge, a growing drive for independence, and a second wave of separation anxiety. Many toddlers start resisting bedtime, calling out overnight, or fighting naps. It typically passes within 2 to 6 weeks when routines stay steady.

Sleep Regression Calculator: your baby's timeline