Most sleep experts recommend waiting until at least 4 months old before letting a baby cry it out, with many pediatricians preferring closer to 6 months. Before 4 months, babies lack the biological development needed to sleep through the night or calm themselves without help.
Why 4 Months Is the Earliest Starting Point
A newborn’s brain simply isn’t wired for self-soothing. Babies are born without a functioning internal clock. Their circadian rhythm, the system that distinguishes day from night and regulates sleep hormones, doesn’t even begin developing until around 2 to 4 months of age. It won’t be fully established until 12 months or later. Without this biological foundation, a young baby can’t consolidate sleep into long stretches no matter how long you let them cry.
Around 4 months, several things change at once. Sleep cycles start to mature, the circadian rhythm kicks in (with some fits and starts), and many babies develop the neurological capacity to learn self-soothing. As a pediatrician at UNC Health puts it, there’s solid data showing that by 4 months, a baby’s brain and body are ready for this skill. That said, some doctors recommend waiting until 6 months, when nighttime caloric needs have dropped further and the baby is more developmentally robust.
The Sleep Regression That Signals Readiness
Ironically, one of the clearest signs your baby is ready for sleep training looks like the opposite of progress. Between 4 and 6 months, most babies go through a sleep regression where they start waking up more frequently than before. This isn’t a setback. It means their sleep cycles are maturing from the short, simple cycles of a newborn into the longer, more complex patterns of adult-like sleep. During these transitions between sleep cycles, they briefly wake up and haven’t yet learned how to drift back off on their own.
Other readiness signs include your baby being able to roll over, showing some ability to find a comfortable position in the crib, and no longer needing to eat every few hours overnight. If your baby is formula-fed and over 6 months, nighttime hunger is unlikely to be the reason for wake-ups, since formula digests more slowly than breast milk. For breastfed babies, the picture is a bit different, and some may genuinely need a feeding well past 6 months.
Night Feedings and When Babies Outgrow Them
One reason you can’t let a very young baby cry it out is that they’re often crying because they’re hungry. Newborns have tiny stomachs and need to eat every few hours around the clock. The timeline for dropping night feeds depends partly on how your baby is fed.
Formula-fed babies can typically go without nighttime feeds starting around 6 months. Breastfed babies may need night feeds longer, with full night weaning generally considered appropriate from around 12 months. This doesn’t mean you can’t sleep train a breastfed baby at 4 or 6 months. It just means you might still need to include one or two scheduled feeds overnight while teaching them to fall asleep independently at bedtime and after non-hunger wake-ups.
Cry It Out vs. Graduated Methods
When people say “cry it out,” they usually mean one of two approaches. Full extinction means putting the baby down drowsy but awake, saying goodnight, and not returning until morning (or until a scheduled feed). Graduated extinction, often called the Ferber method, follows the same principle but includes brief check-ins at increasing intervals. You might check after 3 minutes the first time, then 5, then 10, gradually stretching the gaps each night.
During check-ins, you don’t pick the baby up. You offer brief verbal comfort, maybe a gentle shush or a quiet phrase, then leave again. The visits are meant to reassure both you and the baby, not to fully soothe them to sleep. Some families find that check-ins actually make crying worse because the baby gets frustrated when you leave again. Others find the gradual approach more tolerable emotionally. Neither method is universally better; both work on the same principle of giving your baby space to learn a new skill.
What the First Few Nights Look Like
The first night is almost always the hardest. Crying on night one varies enormously from baby to baby. Some settle in under 15 minutes. Others cry for an hour or two, and in some cases longer. There’s no way to predict where your baby will fall on that spectrum.
The pattern most families report is a steep drop-off. A baby who cries for an hour on night one might cry for 20 minutes on night two and under 10 minutes by night three. Some babies have an “extinction burst” around night three or four, where crying temporarily spikes before dropping again. This is normal and doesn’t mean the process has failed. By the end of the first week, most babies are falling asleep with minimal or no crying.
The Stress and Attachment Question
The most common worry parents have is whether letting a baby cry will cause lasting emotional harm. When a baby cries alone, their body does produce cortisol, the stress hormone. Sustained high cortisol in infancy is associated with negative effects on brain development and stress regulation. This is the kernel of truth behind the concern, and it’s why sleep training a very young newborn is genuinely not recommended.
However, the research picture is more nuanced than the debate online suggests. No long-term study has found that sleep training at an appropriate age damages the parent-child bond or causes lasting psychological harm. At the same time, there hasn’t been a rigorous longitudinal study tracking attachment outcomes in sleep-trained families over many years. What the existing evidence shows is that short-term cortisol spikes during a few nights of sleep training in a 5- or 6-month-old, who otherwise has a warm and responsive caregiving environment, are different from the chronic, unresponsive neglect that genuinely harms development.
The American Academy of Pediatrics acknowledges that babies 6 months and older will wake at night and that giving them a few minutes to resettle on their own is a normal part of sleep development. Their guidance explicitly says not to rush in immediately when a baby cries at night, while also noting that you should respond when there’s an actual need like hunger, a dirty diaper, or illness.
When to Hold Off
Sleep training works best with a healthy baby in a stable routine. You’ll want to wait or pause if your baby is sick, teething badly, or going through a major transition like starting daycare or traveling. Premature babies should be evaluated based on their adjusted age (calculated from their due date, not their birth date), which may push the timeline back.
Trust your instincts during the process. If your baby’s cry sounds different from their usual protest cry, something sharper or more distressed, it’s reasonable to go in and check. Sleep training doesn’t require you to ignore signs of genuine discomfort or illness. The goal is teaching your baby to fall asleep independently, not to stop responding to them altogether.