You are running on broken sleep. You have read three different articles that all say something different. One tells you to start at 4 months. Another says wait until 6. A third says you will know when the time is right — which tells you absolutely nothing when you are staring at the ceiling at 2am for the fourth night in a row.

Here is the truth: sleep training readiness is not just about age. It is about a combination of physical, neurological, and behavioral signs that show up at different times for different babies. Some babies show readiness at 4 months. Others are not ready until closer to 7 or 8 months. And starting before those signs are present — regardless of what the calendar says — almost always makes the process harder, longer, and more stressful for everyone.

This article breaks down exactly what to look for, by age and by milestone. Not vague advice. Specific signs.

Why Timing Matters More Than the Method You Choose

Most of the sleep training debate centers on which method to use. Ferber versus fading versus no-cry. That debate, while valid, skips over something more important: none of those methods work well if your baby’s nervous system is not ready for them yet.

Babies do not exhibit a robust circadian rhythm until 6 to 12 weeks of age, after which it strengthens gradually, leading to greater nighttime sleep consolidation over time. Before that rhythm is established, asking a baby to self-settle is like asking someone to sleep on a schedule when their body clock does not exist yet. It is not stubbornness. It is biology.

By 4 to 6 months of age, infants develop a more typical sleep cycle that reflects three states: wake, non-rapid eye movement sleep, and rapid eye movement sleep. This is the shift that makes sleep training possible. Before it happens, babies cycle through sleep differently — and the strategies that work after this shift simply do not apply beforehand.

Due to the developmental nature of infant sleep consolidation, behavioral approaches to foster independent sleep initiation have been recommended to be implemented around 5 to 6 months of age. That does not mean 5 to 6 months is the only window. It means that is when the biology catches up with the behavior you are trying to teach.

Timing the start correctly means less crying, faster results, and a baby who adapts instead of one who is pushed past what their nervous system can currently do.

The 3 Things That Must Be True Before You Start

Before looking at age-specific signs, three things need to be in place for any baby at any age. These are non-negotiable starting points.

Your baby is gaining weight consistently. This is the most important check. In general, 4 months and 14 pounds is a good benchmark. Babies do not develop their own melatonin or regulation of their sleep cycles until around 3 months or later. Generally, 14 pounds is a good weight because the baby may not need overnight feedings at that point. If your baby is not yet at a weight where their pediatrician is comfortable reducing night feeds, sleep training is not appropriate yet. Night waking that is driven by genuine hunger is not a sleep problem — it is a feeding need.

Your pediatrician has cleared you. The AAP advises that sleep training should not begin until your baby has returned to birth weight and your pediatrician has cleared them for longer stretches between feedings. For some babies, especially those with reflux, feeding challenges, or developmental variations, 6 months may be a more realistic starting point. If your baby was premature, has reflux, or has been flagged for slow weight gain, always get explicit clearance before reducing any night feeds or beginning formal sleep training.

You can commit to consistency for at least 10 to 14 days. This is about you, not your baby. The best sleep training method is the one you and your partner can maintain until the pattern becomes habit. Inconsistency can stop any progress being made. Your baby is looking to learn and needs to understand what to expect. If a work trip, a family visit, or a major schedule disruption is coming in the next two weeks, wait until after it passes.

Signs Your Baby Is Ready: The 4 to 5 Month Window

Four months is the earliest most pediatric sleep experts recommend considering sleep training, and only when specific signs are present alongside the weight and medical clearance criteria above.

Your Baby Has Hit the 4-Month Sleep Regression

This sounds counterintuitive — why would worse sleep mean your baby is ready? Because the 4-month regression is not actually a regression. It is a permanent neurological shift.

Around the 3 to 4-month mark, a major biological shift occurs. Your baby’s sleep cycles begin to mature into three distinct non-REM stages, mirroring adult sleep architecture. Sleep cycles lengthen to 50 to 60 minutes, and their circadian rhythm begins to mature. Before this shift, your baby was cycling through sleep differently. After it, they are cycling the same way they will for the rest of their life — which means they now have the neurological hardware to learn independent sleep skills.

If your baby was sleeping in a fairly predictable pattern and then suddenly started waking more frequently around 3 to 4 months, that shift is the sign. The sleep architecture changed. Now it can be worked with.

Your Baby Can Stay Awake for 1.5 to 2 Hours Without Falling Apart

A baby is likely ready when you notice they can stay awake and alert for stretches of 1.5 to 2 hours without immediately becoming overtired.

This matters because it tells you something about their nervous system’s capacity for regulation. A baby who crashes into hysterical overtiredness after 40 minutes of wake time does not yet have enough self-regulation capacity to manage the settling process. A baby who can handle a fuller wake window — playing, feeding, interacting, and then showing sleepy cues — has a more mature regulatory system. That maturity is what sleep training builds on.

Watch for sleepy cues that appear at a predictable point in the wake window: eye rubbing, reduced eye contact, slowing of movement, yawning. Cues that come at roughly the same point each time show a developing internal rhythm.

Your Baby Is Starting to Self-Soothe in Small Ways

Most infants develop the neurological capacity to self-soothe between 4 and 6 months. Physical signs like hand-to-mouth behavior and rhythmic movement are positive developmental indicators. By 4 months, the brain begins to produce its own melatonin, allowing babies to bridge sleep cycles without parental intervention, provided their sensory environment supports it.

Look for your baby bringing their hands to their mouth when drowsy. Look for rhythmic movements — head turning side to side, gentle leg thumping, sucking on fingers. These are not random. They are your baby’s nervous system learning to generate its own calming input. They are the earliest signs that self-settling is becoming biologically possible.

Night Feeds Are Getting Less Urgent

At 4 to 5 months, a baby who genuinely needs calories at night will wake crying with urgency and feed hungrily for a full feed. A baby who is beginning to wake out of habit — not hunger — may wake and fuss at a lower intensity, feed briefly or lazily, and go back down quickly.

You cannot sleep train hunger. But you can sleep train habit. If at least one of your baby’s nighttime wake-ups looks more like habit than need, that is a readiness signal worth paying attention to.

Signs Your Baby Is Ready: The 5 to 6 Month Window

This is the window where most babies show the clearest readiness signs, and where the research most consistently supports starting.

Your Baby Has a Predictable Nap Pattern

At 5 to 6 months, most babies are settling into a two-nap structure — one in the morning and one in the afternoon. The exact timing will vary, but if you can roughly predict when your baby will be tired based on their wake time, that predictability signals a maturing circadian rhythm.

By 3 to 4 months the circadian rhythm becomes more established, leading to more consolidated nighttime sleep. By 6 to 8 weeks, babies begin to produce melatonin, a hormone that promotes sleep, with melatonin levels naturally increasing in response to darkness. By 5 to 6 months, this system is developed enough that a consistent schedule starts to sync with it rather than fight it.

If your baby’s sleep is completely unpredictable from day to day with no pattern at all, establishing a basic nap routine before sleep training the nights will make everything go more smoothly.

Your Baby Shows Clear Sleepy Cues Before They Are Overtired

There is a difference between sleepy and overtired. A baby who is sleepy is giving you a window. A baby who is overtired has already passed it, and the stress hormones that kick in to keep them going will work against any settling attempt.

By 5 to 6 months, a baby who is ready for sleep training will have readable, consistent cues in the sleepy window: decreased engagement with toys or faces, a slower, quieter quality to their movements, pulling at their ears, brief eye rubbing, or a glassy, unfocused look. These cues appear before crying. A baby who goes from happy to hysterical with no middle ground is either being kept up too long or is not quite ready for the settling process yet.

Your Baby Can Be Put Down Drowsy and Not Immediately Panic

Try this test. After your full bedtime routine — bath, feed, book, whatever you do — put your baby in the crib drowsy but awake. Not asleep. Not screaming. Somewhere in between.

Watch what happens in the first 30 to 60 seconds. A baby who fusses mildly, looks around, and makes some attempt to settle — even if they do not succeed — is showing readiness. A baby who immediately escalates to full distress with zero attempt at self-calming is showing you that the self-regulation piece is not there yet.

You do not need your baby to succeed at self-settling to start. You need them to try.

Daytime Feeds Are Established and Predictable

By 5 to 6 months, most babies are feeding every 3 to 4 hours during the day. Most doctors will agree that you can stop intentionally waking your baby for night feedings around 3 to 4 months as long as they are showing stable weight gain and staying on their growth curve. However, some babies will not be able to sleep through the night without any feedings until closer to 9 months.

If your baby is taking full, adequate feeds during the day and their weight is on track, the case for continuing multiple night feeds becomes less about nutrition and more about habit. That distinction — need versus habit — is the key question at this stage, and it is one worth discussing directly with your pediatrician.

Signs Your Baby Is Ready: The 6 to 8 Month Window

Some babies are simply not ready until 6 months or later. This is not a problem. Later starters often progress faster because their self-regulation skills are more developed.

Your Baby Understands Object Permanence

Around 6 months, babies begin developing object permanence — the understanding that things still exist even when they cannot see them. This is why separation anxiety often spikes around this time. But it is also why sleep training at this age can be more effective in certain ways: your baby now understands that when you leave the room, you still exist and will come back.

Before object permanence develops, a baby does not understand that you are coming back. After it develops, your baby can begin to build the emotional understanding that your absence at bedtime is not permanent. That understanding underpins the success of any sleep training method that involves parental departure from the room.

Your Baby Has a Strong Attachment and Responds to Your Comfort

There is no evidence that sleep training harms the bond between caregivers and babies. Responsive, loving care during the day continues to support strong attachment, regardless of the sleep approach used.

A baby who has a clear, secure attachment to you — who calms quickly when you pick them up, who seeks your face when unsure, who responds strongly to your voice — is actually a better candidate for sleep training, not a worse one. That secure attachment is the foundation that makes learning to self-settle possible. It means your baby has enough trust in their environment to tolerate the discomfort of learning.

Night Waking Has Become a Clear Pattern

By 6 to 8 months, a baby who is waking at remarkably consistent times each night — say, 11pm and 2am and 5am, every single night — is demonstrating habitual waking rather than need-based waking. The consistency is the tell.

Need-based waking is more variable. It depends on how much the baby ate during the day, how much activity they had, whether they are in a growth spurt. Habitual waking is like clockwork. If you can set your watch by your baby’s nighttime wake-ups, that regularity is a strong sign that the waking is being driven by expectation and association rather than genuine need.

Signs That Tell You to Wait — Even If the Age Feels Right

Age alone is not enough. These situations call for waiting regardless of what month your baby is in.

Your baby is sick or has been recently sick. Any illness — even a mild cold — disrupts sleep in ways that have nothing to do with habits or associations. Wait at least one full week after your baby is symptom-free before starting.

A major change just happened or is coming. Starting daycare, moving house, a new sibling, travel — any of these will destabilize sleep independently. Starting sleep training during or immediately around a major transition stacks two challenges on top of each other. Wait for a calm two-week stretch.

Your baby is in a developmental leap. Sleep regressions often line up with major milestones that make it harder for babies to settle and stay asleep: increased mobility like rolling or sitting can cause restlessness at 6 months, and crawling, standing, and separation anxiety may interrupt sleep between 8 and 10 months. If your baby is actively learning a new physical skill — rolling, sitting, pulling to stand — their brain is working overtime during sleep to consolidate that learning. This is not the moment to add the additional challenge of learning to self-settle.

Your baby is teething acutely. Mild teething discomfort is manageable. A baby with a swollen, clearly painful gum who is genuinely suffering is not in a state where sleep training is kind or effective. Wait for the acute phase to pass.

Your gut says something is wrong. Excessive night waking alongside poor weight gain, breathing irregularities, or persistent reflux symptoms needs medical investigation before any behavioral approach is tried. Sleep training does not fix a medical problem. It just adds stress on top of one.

The One Sign Parents Almost Always Miss

You are ready.

That sounds obvious, but it is not. Sleep training requires consistency across multiple nights — including the hard nights, the nights where your baby cries longer than expected, the nights where you question everything. Parents who start before they are emotionally prepared to follow through often stop partway, restart, stop again, and end up with a baby who is more confused and a process that takes three times as long.

Ask yourself these questions honestly. Can you handle your baby crying for 20 to 40 minutes without intervening? Do you and your co-parent agree on the method and the plan? Are you prepared to keep nighttime interactions brief and consistent even at 3am? Can you stay the course for two weeks without caving on the hard nights?

Sleep training requires several consecutive days and nights of consistency. A baby who shows readiness signs will almost always respond faster and with less distress than one who does not. But even a ready baby needs a consistent parent. The research is clear that the method matters far less than the consistency with which it is applied.

If your answer to any of those questions is uncertain, spend a few days building a concrete plan before you start. Write down your method. Agree on who handles which nights. Decide in advance what you will do if your baby cries for longer than you expected. Having that plan means you are making decisions before exhaustion and emotion cloud your judgment.

A Quick Reference: Readiness by Age

3 months and under: Not ready. The circadian rhythm is not yet established. Night waking is biologically driven. Focus on feeding, connection, and a consistent bedtime routine rather than formal sleep training.

4 months: Possibly ready if the 4-month sleep regression has hit, weight is above 14 pounds, pediatrician has cleared you, wake windows are extending to 1.5 to 2 hours, and early self-soothing behaviors are visible.

5 to 6 months: The primary readiness window for most babies. Nap patterns are emerging, sleepy cues are readable, daytime feeds are established, and the nervous system is mature enough to support the self-settling process.

6 to 8 months: Strong readiness window, especially for babies who were not ready earlier. Object permanence adds a new layer of understanding that supports the process. Separation anxiety may increase at this stage — this does not mean you should not sleep train, but choose a method that involves check-ins if separation anxiety is high.

8 months and beyond: Still completely appropriate. Some babies, particularly those with high sensitivity, slower nervous system maturation, or medical complications in early infancy, simply take longer to reach readiness. A later start is not a failure. It is a match to your baby’s developmental pace.

What to Do With This Information Tonight

You do not need every single sign on this list to appear before you start. You need enough of them — particularly the medical clearance, the weight, and the neurological maturity signals — to feel confident that your baby has the capacity to do this.

If you checked most of the signs for your baby’s age window, talk to your pediatrician at the next appointment. Confirm the weight and feeding picture. Ask explicitly whether nighttime feeds are still nutritionally necessary. Then pick a two-week window with no travel, illness, or major disruption on the horizon.

Then start.

The goal is not a perfect baby who never wakes. The goal is a baby who can find their way back to sleep without needing you to do it for them. That skill — once learned — makes every night better. For them and for you.