When are the sleep regression ages?

Commonly around 4 months, 6 months, 8-10 months, 12 months and 18 months, and sometimes around 2 years. Not every baby has them.

How long does a sleep regression last?

Usually 2 to 6 weeks. If disrupted sleep lasts much longer or comes with illness signs, talk to your pediatrician.

Is the 4-month sleep regression real?

The changes are real: around 4 months, sleep becomes more adult-like, with lighter phases where babies wake more easily. 'Regression' is a popular term rather than a medical one.

Should I use corrected age for regressions?

Yes, for babies born early, developmental changes tend to follow corrected age.

Do sleep regressions mean I should start sleep training?

Not necessarily. Many families wait until the regression passes. Talk to your pediatrician about approaches that suit your baby and family.

Sleep Regression Calculator: Ages & Dates / Tot

Medically reviewed by Safi Ullah Khan · Written by Muneeb Rana · Last updated 21 October 2026

Quick answer: A sleep regression calculator shows when your baby reaches the ages parents most often report sleep setbacks: around 4 months, 6 months, 8-10 months, 12 months and 18 months. Each usually lasts 2-6 weeks. 'Sleep regression' isn't a medical diagnosis; it describes normal developmental changes that briefly disrupt sleep.

TL;DR

Enter a birth date (or due date for preemies) to see likely date ranges.
The 4-month change is the best known: sleep cycles become more adult-like.
Keep routines steady; rule out illness, hunger and teething.

This sleep regression calculator turns your baby's birth date into the calendar dates when common sleep setbacks tend to happen, so you're not caught off guard. It also lists what's usually going on developmentally at each age and what tends to help.

How to use the sleep regression calculator

Enter your baby's birth date. For babies born early, enter the due date (corrected age).
Read the date ranges for each common regression age.
Tap an age to see what typically changes and tips.
Add a reminder to your calendar if you like.

How the sleep regression calculator works

for each age A in [4, 6, 8-10, 12, 18] months:
    window_start = birthDate + (A - 0.5) months
    window_end   = birthDate + (A + 1) months

Age	What's often going on	Typical length
About 4 months	Sleep cycles mature; more alert, rolling	2-6 weeks
About 6 months	Sitting, babbling, nap changes	1-3 weeks
8-10 months	Crawling, pulling up, separation anxiety, 3→2 naps	2-6 weeks
About 12 months	Walking, first words, nap resistance	1-3 weeks
About 18 months	Independence, teething molars, separation anxiety	2-6 weeks

These ages come from common parent and pediatric-practice reports, not from AAP or NHS guidance; many babies have none of them.

Worked example

Hana was born on 10 June 2026. The tool shows a likely 4-month window from about 26 September to 10 November 2026. When she starts waking every 2 hours in October, her parents recognise it, keep her routine steady and log sleep in Tot to see when it eases.

What helps during a regression

Keep the bedtime routine the same, offer plenty of practice time for new skills during the day, watch wake windows (overtired babies sleep worse), and respond calmly at night. The NHS suggests a consistent bedtime routine from around 3 months. Avoid starting new sleep habits you don't want to keep.

When it might be something else

Ear infections, colds, reflux, hunger during a growth spurt and teething can all disrupt sleep. Call your pediatrician if your baby has a fever, seems in pain, snores loudly, has breathing pauses, or sleep doesn't improve after several weeks. Read baby fever: when to call.

Track it so you know when it's over

A sleep log turns 'every night is awful' into data. Tot's baby sleep tracker shows daily totals and trends, so you can see when night wakings drop again. See also the 4-month sleep regression.

Download Tot free on the App Store or Google Play. Free with ads; optional Premium.

Sources

AAP HealthyChildren.org: Getting Your Baby to Sleep: www.healthychildren.org (accessed 21 October 2026)
AAP HealthyChildren.org: Healthy Sleep Habits, How Many Hours Does Your Child Need?: www.healthychildren.org (accessed 21 October 2026)
NHS: Helping your baby to sleep: www.nhs.uk (accessed 21 October 2026)
AAP HealthyChildren.org: How to Keep Your Sleeping Baby Safe (AAP policy explained): www.healthychildren.org (accessed 21 October 2026)

Medical disclaimer:

Tot and this website give general information only. Feeding, sleep and growth ranges vary; always follow your pediatrician's advice. If your baby is unwell, contact your doctor or emergency services.

Sleep Regression Calculator