How to Train Your Baby to Sleep Through the Night

Most healthy babies can sleep for a stretch of six to eight hours by around six months of age, but getting there involves a mix of biological readiness, consistent habits, and a sleep environment that supports longer stretches. “Sleep training” is really an umbrella term for several different approaches, and the evidence behind them is stronger and more reassuring than many parents expect. That said, a significant number of babies at six and even twelve months still do not sleep through the night by any definition, so the timeline varies more than the parenting advice industry typically admits.

What “Sleeping Through the Night” Actually Means

Before you pick a strategy, it helps to know that researchers and parents often mean very different things by “sleeping through the night.” The classic scientific definition, dating back decades, counted a baby as sleeping through if they stayed quiet from midnight to 5 a.m. That is only five hours. More recent work uses stricter benchmarks: six hours of uninterrupted sleep, eight hours, or sleeping from roughly 10 p.m. to 6 a.m. to match a family’s schedule. A review of the research found that most infants can manage eight continuous hours by six months and nine or more hours after that, though the older five-hour definition probably underestimated what babies are capable of.¹

Still, “most” is doing a lot of work in that sentence. A large longitudinal study found that roughly 28% to 57% of babies at six and twelve months were not sleeping through the night, depending on whether the benchmark was six or eight hours.² That same study found no connection between sleeping through and a baby’s mental or motor development, or the mother’s mood. In other words, if your baby is not there yet, it does not mean something is wrong with either of you.

Why Babies Are Not Built to Sleep All Night From the Start

Newborns spend about 70% of their time asleep, but those sleep episodes are scattered evenly across day and night with no real pattern. At two weeks, a baby sleeps in roughly four-hour chunks. A recognizable circadian rhythm, where the body starts distinguishing day from night, does not begin to appear until around five weeks and does not consolidate until about fifteen weeks. By six to nine months, most infants display at least six hours of consolidated nighttime sleep.³ Total sleep across the first year averages about fourteen hours a day. What changes is not how much the baby sleeps but when: longer stretches shift to nighttime while daytime wakefulness increases.

This means that sleep training before about three to four months is largely futile because the underlying biology is not ready. The circadian clock has to mature before a baby can reliably tell night from day, and no behavioral technique overrides that developmental timeline. Most pediatric sleep researchers suggest waiting until at least four months, and many say six months, before starting any formal approach.

The Main Sleep Training Methods

The phrase “sleep training” covers several distinct approaches, and they are not all the same emotionally or practically. The common thread is teaching the baby to fall asleep independently at bedtime so that when they naturally wake during the night (as all humans do between sleep cycles), they can put themselves back to sleep without a parent’s help.

Graduated extinction: You put the baby down awake and leave the room, then return at increasing intervals to briefly reassure them without picking them up. The intervals might start at two minutes, then five, then ten. Over several nights, the intervals lengthen and the baby learns to settle without you present. This is what most people picture when they hear “sleep training.”
Bedtime fading: You temporarily push the baby’s bedtime later to match the time they are actually falling asleep, then gradually move it earlier. The idea is to reduce the struggle at bedtime by starting from a point of high sleep pressure.
Full extinction: You put the baby down and do not return until morning (or until a scheduled feed). This is the most controversial approach because it involves extended periods of crying with no parental check-ins.
Scheduled awakenings: You wake the baby before they would typically wake on their own, then help them fall back asleep. Over time, you phase out the preemptive waking.

A systematic review of the evidence found solid research support for graduated extinction, bedtime fading, and scheduled awakenings as effective behavioral treatments for infant sleep problems.⁴ Full extinction works too, in the sense that crying eventually stops and babies sleep longer, but the emotional toll on parents is high enough that many families abandon it partway through, which can actually make things worse.

Does Sleep Training Harm Babies?

This is the question that keeps parents up at night (figuratively, on top of literally). The short answer from the available evidence is no. A randomized controlled trial comparing graduated extinction and bedtime fading to a control group found that both methods improved sleep, and at twelve months there were no differences between groups in emotional or behavioral problems and no differences in attachment security.⁵

A five-year follow-up of a separate randomized trial examined children’s emotional and behavioral scores, sleep habits, stress levels, parent-child closeness, and parenting style. There were no differences between families who had received a sleep intervention in infancy and those who had not, on any measure.⁶ The children were not more anxious, their relationships with their parents were not worse, and their cortisol (stress hormone) levels were normal.

Critics point out that long-term studies are still relatively few and that most research measures outcomes the researchers chose to look at, potentially missing subtler effects. The concern about leaving a baby to cry is not unreasonable on its face, and some researchers have questioned whether the pursuit of extinction-based methods is always necessary given that alternatives exist.⁷ But the controlled trials we do have consistently show no measurable harm. If you choose to sleep train, the data suggests your baby will be fine.

How Sleep Training Affects Parents

One often-overlooked piece of the puzzle is what happens to the adults. Sleep deprivation grinds down parental mental health, and there is solid evidence that addressing infant sleep problems has cascading benefits. A population-based trial found that mothers who received a sleep intervention when their babies were young were significantly less likely to report depression symptoms two years later: about 4% in the intervention group hit clinical thresholds compared with about 13% in the control group.⁸

Another study found significant reductions in depression, anxiety, and stress after an infant sleep intervention. At baseline, about a third of mothers scored as mildly depressed or above; after the intervention, that dropped to 5%.⁹ Responsive approaches (where a parent stays more involved rather than leaving the room entirely) have also shown drops in maternal stress and depression, suggesting that the benefits are not exclusive to extinction-style methods.¹⁰

Feeding, Calories, and Night Waking

A persistent piece of advice is that feeding the baby more during the day, or introducing solids, will stop night wakings. The reality is more nuanced. Research found that infants who received more milk or solid feeds during the day were less likely to feed at night but were not less likely to wake up.¹¹ So you might eliminate the night feed, but the baby may still wake and need comfort for other reasons.

Breastfeeding adds another wrinkle. A study tracking sleep trajectories found that fully breastfed infants actually had longer total night-sleep durations at six, nine, twelve, and twenty-four months than formula-fed infants, even though breastfed babies woke more often between six and twelve months.¹² The frequent wakings may partly reflect an evolutionary pattern: one hypothesis is that night waking and nursing evolved to extend the gap between pregnancies by maintaining lactational amenorrhea, which historically improved infant survival.¹³ Whatever the evolutionary reasoning, the practical point is that breastfed babies waking at night is biologically normal and does not mean breastfeeding is “causing” a sleep problem.

Light, Darkness, and the Circadian Clock

One of the simplest and most under-discussed tools for helping a baby sleep longer at night is light exposure during the day. A study of six- to twelve-week-old infants found that babies who slept well at night had been exposed to significantly more light during the early afternoon.¹⁴ This makes biological sense: light is the primary cue that sets the circadian clock, and a baby who spends most of the day in dim indoor lighting gets weaker signals about when day ends and night begins.

A scoping review confirmed that cycled lighting, meaning bright light during the day and dim conditions at night, improves nighttime sleep and daytime wakefulness in infants.¹⁵ The practical takeaway: get outside with your baby during the day, keep lights bright indoors when the sun is up, and dim them substantially in the hour or two before bedtime. Use as little light as possible during nighttime feeds and diaper changes. You are essentially teaching the baby’s clock what “daytime” looks like.

Where Your Baby Sleeps Matters

The American Academy of Pediatrics recommends room-sharing for at least the first six months to reduce the risk of SIDS, but the data on room-sharing and sleep quality tells an interesting and somewhat complicated story. In the INSIGHT study, babies who moved to their own room early had better sleep consolidation at four months, sleeping in stretches about 46 minutes longer than room-sharers. By nine months, early independent sleepers were getting 40 more minutes of total nighttime sleep. That advantage persisted: at two and a half years, babies who had been sleeping independently by nine months still slept more than 45 minutes longer per night than those still room-sharing at nine months.¹⁶

A longitudinal study tracking families from three to eighteen months found that mothers who persistently room-shared had lower sleep quality themselves, with shorter longest sleep periods and more night wakings than mothers whose babies slept alone. For infants, the biggest difference was also in longest sleep period: room-sharing babies had shorter continuous stretches.¹⁷ The likely mechanism is straightforward: when parent and baby are in the same room, every small noise the baby makes can trigger an intervention, and every sound the parent makes can wake the baby. Once you move past the recommended room-sharing period, transitioning the baby to their own space often improves sleep for everyone.

White Noise and Other Sleep Aids

White noise machines have become nearly universal in nurseries, and the evidence does support their use with a caveat about volume. A meta-analysis of randomized trials found that white noise reduced the number of infant awakenings during both 24-hour and 12-hour nocturnal periods and significantly increased nighttime sleep efficiency.¹⁸ A separate trial in premature infants found that white noise increased sleep duration by about two hours and improved sleep efficiency.¹⁹

The concern is intensity. A scoping review found that some white noise machines can exceed 91 decibels at maximum volume, which is above what occupational safety guidelines consider safe for even a two-hour adult work shift. Animal studies have shown harmful effects from continuous moderate-intensity white noise on early brain development, though low-intensity exposure may be beneficial.²⁰ The reasonable approach is to keep the machine at the lowest volume that effectively masks household sounds, place it well away from the crib, and avoid running it at full blast all night.

Developmental Setbacks Are Normal

Even after a baby starts sleeping well, regression is common and can feel demoralizing. One well-documented trigger is the onset of crawling. A study of seven- and eight-month-olds found that infants who were already crawling had more bedtime difficulties and night waking than pre-crawlers, with locomotion accounting for about 17% of the variation in night waking after controlling for age and sex.²¹ The theory is that each major motor milestone brings a period of cognitive reorganization that temporarily disrupts sleep. Parents often see similar regressions around standing, walking, and language bursts. These periods typically last a few weeks and resolve without needing to restart sleep training from scratch, though you may need to be more consistent about your existing routines during them.

Medical issues can also masquerade as behavioral sleep problems. Gastroesophageal reflux, both the visible spit-up kind and silent reflux without obvious regurgitation, was found to be a frequent cause of sleep interruptions in infants studied with esophageal monitoring. Silent reflux proved equally disruptive to the obvious kind.²² If your baby is sleeping poorly despite consistent training and there is no obvious developmental explanation, it is worth discussing reflux, ear infections, or other discomfort with your pediatrician before assuming you are doing something wrong.

Temperament and Individual Variation

Not every baby responds to sleep training the same way, and temperament plays a real role. Research tracking infants from one to six months found that babies with high “surgency” (a trait characterized by high activity, excitability, and positive emotion) responded more dramatically to maternal emotional availability at bedtime. Highly surgent babies whose mothers were warm and responsive at bedtime showed a greater increase in sleep time than other infants.²³ In other words, temperament can amplify or dampen the effect of whatever approach you take. An easy-going baby might settle quickly with minimal intervention. A high-energy, highly reactive baby might need more parental presence and warmth at bedtime to make the same gains.

The large individual variation in sleep development that researchers consistently note is worth keeping in mind.³ Some babies consolidate sleep early with almost no parental effort. Others need months of consistent work. Comparing your baby’s sleep to another baby the same age is almost always misleading, because the range of normal is genuinely enormous.

Cultural Context Shapes Expectations

What counts as a “sleep problem” depends heavily on where you live. A large cross-cultural study comparing predominantly Asian and predominantly Caucasian countries found dramatically different norms. Children in Asian countries had later bedtimes, shorter total sleep, and much higher rates of bed-sharing. Bed-sharing ranged from about 6% in New Zealand to 83% in Vietnam. The percentage of parents who perceived their child had a sleep problem ranged from 11% in Thailand to 76% in China.²⁴

A multinational study comparing Korea, the United States, and Australia found that Korean infants had shorter nighttime sleep and took longer to fall asleep at all time points studied, yet bed-sharing was associated with lower insomnia symptoms among Korean mothers at 24 months.²⁵ The point is not that one culture has it right and others have it wrong. Sleep training as a concept is largely a product of Western, individualistic parenting culture where babies are expected to sleep alone in their own room. In many parts of the world, the “problem” of night waking is managed by bed-sharing and responsive nursing through the night, and that arrangement works for those families. Your goals for your baby’s sleep should reflect what your family actually needs, not an idealized version of infant sleep borrowed from a culture that might not be your own.

Wearable Monitors and Tracking Apps

The explosion of infant sleep monitors, from sock-style pulse oximeters to camera-based breathing trackers, has created a new layer of both reassurance and anxiety. A large survey of parents using these devices found that when the technology worked well, the most common mental health benefit was reduced anxiety and “peace of mind,” reported by about 23% of users, followed by improved parental sleep.²⁶ But device malfunctions were commonly reported, and when the technology failed or gave false alarms, parents experienced increased stress and disrupted sleep for both themselves and their babies.

Some parents reported making medical decisions based on device output, which raises its own set of concerns since most consumer-grade monitors are not FDA-cleared medical devices. The research on tracking technology suggests it can be helpful for anxious parents when it works reliably, but leaning on it too heavily can create its own cycle of monitoring and worry. If you find yourself checking the app more than you are sleeping, the monitor may be working against you.