Sleep is a moving target. When you were a newborn, you slept for most of the day, then less as an older child; as a teen, you slept later. A senior’s bedtime is earlier—part of a lifetime journey of rising and falling sleep needs depending on age. How much sleep do you need at the various stages of life, and why do our requirements shift all the time?

Newborns and babies

Babies aged zero to three months sleep 14 to 17 hours out of every 24—partly a function of the newborn’s introduction to the world after three trimesters in the darkness of the womb. A large share of time in the womb is spent sleeping, and the reason for so much slumber is the same both before and after birth: growth. Babies triple their weight between birth and one year old, and it’s during sleep—especially the deep cycle called slow-wave sleep—that growth hormone is most prodigiously released. Adding bulk is not the only thing the youngest babies are doing.

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“There are a lot of new neural connections forming,” says Dr. Yi Cai, director of sleep surgery at the Columbia University Irving Medical Center, “and a lot of new learning going on. Everything’s new, and that’s a prominent driver of sleep needs for that age.”

Later in the first year, from four months to 12 months, sleep needs drop slightly, to about 12 to 16 hours, but that’s not because babies are growing less. Rather, Cai says, they are beginning to develop circadian rhythms that connect them to a more common dark-light, day-night cycle.

Toddlers and preschoolers

In the one- to two-year age group, sleep needs drop again to 11 to 14 hours, and fall further, to 10 to 13 hours, from ages three to five. This is due to a somewhat slower growth rate as children move out of babyhood.

Cognitive needs change too. Learning is consolidated when we’re sleeping, and it’s in the first months and year or two of life that we vacuum up the most basic knowledge. “When you’re younger, there’s a lot more relevant learning that goes on,” says Joshua Tal, New York-based sleep and health psychologist. “You’re learning who the people in your life are and what language is.”

By 18 months, toddlers’ need for naps generally decreases to just one per day, lasting from one to three hours, according to the National Sleep Foundation. In the three-to-five-year group, napping during the day may continue to be necessary, especially since the preschooler’s growing imagination may lead to more bad dreams or nighttime fears—monsters under the bed, goblins in the closet—which can disrupt sleep. There are no hard rules here, however, and there can be significant differences from child to child.

“We have some kids that are dropping the nap much earlier than other kids because it’s affecting them at night,” says Tal. “Other kids have very predictable naps.”

Kids and teens

Kids from six to 12 years maintain patterns not unlike preschoolers—with sleep needs falling only slightly, to nine to 12 hours per night—but the need for naps disappears. As puberty hits, however, there is a big change. Thirteen- to 18-year-olds need about eight to 10 hours of sleep per night, but the sleep schedule shifts, with bedtime coming later in the evening and wake-up coming later in the morning. Parents raising teens will commonly notice that the child who once bounded out of bed at 7:00 am on weekends is now sleeping till 11:00. That, says Cai, is because the release of the sleep hormone melatonin changes, occurring later in the evening.

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“A lot of teenagers just have a delayed sleep drive,” she says. “That’s why some teens run into problems with early school times, where they may not get the sleep they need to be up in time for school, and then they might need to catch up on their sleep during the day when they’re back home.”

That, says Tal, is a real problem. “A good kid is finishing their homework and going to bed at 10, and they still have to wake up at around six for school,” he says. “Built into our society there is this devaluation of sleep.”

Adults 

Past the teen years, the body is done growing and the brain is more or less finished developing. That’s when the need for sleep falls to seven or eight hours a night. “There’s less cognitive growth, and it’s more maintenance mode for the body,” says Tal. Adults who need significantly more than eight hours may be suffering from a sleep disorder. Obstructive sleep apnea affects about a billion people worldwide, according to Cai, and is the leading cause of disrupted sleep.

“The upper airway or the throat is collapsing over the course of the night and people have these micro-awakenings because they stop breathing and their body wakes them up to take a breath,” she says. “That can lead to really poor quality sleep and non-refreshing sleep.”

Other people may suffer from hypersomnia, an excessive need for sleep that is not satisfied by logging even ten hours at night and taking naps during the day. The cause of hypersomnia is unclear, though treatments—including stimulant medications and lifestyle changes such as avoiding caffeine and exercise before bed—may help.

Seniors

For people 65 and older, the release of melatonin slows, leading to a bit less sleep as well as lighter sleep. “Circadian rhythms also advance,” says Tal, “so seniors go to bed earlier and they wake up earlier.” Age-related physical changes, such as prostate problems in men that lead to frequent bathroom trips during the night, can also have an impact on deep and steady sleep.

For people who are having a hard time sleeping the right amount of hours for their age group, Cai says, consulting a sleep doctor might be in order. “It’s always worthwhile to see a specialist if there are any significant struggles,” she advises.