FAQ: How much sleep do I need?
The number one question I get from patients, friends, and strangers is, “How much sleep do I need?” Since I’m a scientist and appreciate how scientific journal articles summarize themselves in the abstract (aka TLDR) at the top, here you go:
7-9 hours of regularly-timed, high-quality sleep.
The real question:
Over the years, I’ve realized that usually there’s a different, “real” question hidden behind “How much sleep do I need?” Questions like:
I want/need to do other things, what’s the least amount of sleep I can get by with, without harming my health?
And related: I want to have a sleep “bank account” so I can sleep in on weekends and sleep less during the week. What’s the minimum daily deposit?
I spend a lot of time in bed, so why am I still tired?
I can’t sleep, why can’t I sleep?
My spouse/partner sleeps more/less/differently than I do. Can you give me some ammo to help me make them change?
How can I “hack” my sleep?
We’ll get to those other questions in other posts, so please check back! But for now, here’s the long answer on sleep duration, with data.
Why Too Little Sleep Is Harmful
The National Sleep Foundation released their 2025 Sleep In America survey results, and 6 out of 10 Americans are not getting the recommended amount of sleep! We all know how crummy we feel the next day if we don’t get enough sleep, regardless of how much caffeine (or unfortunately in some cases, stimulant drugs, legal and not) is ingested the next morning. Unfortunately, insufficient sleep has long term health consequences too.
Regularly getting less than 7 hours per night has been linked to:
Shorter lifespan
Impaired cognition and risk of dementia
Weakened immune function
Higher risk of obesity, diabetes, and heart disease
Increased risk of depression and anxiety
Greater likelihood of accidents
So a short night here and there may be unavoidable, but being a habitual 4-hour sleeper is nothing to brag about. Chronic sleep deprivation makes people less able to even feel that they are fatigued, and sets the stage for serious long-term health consequences.
Why Too Much Sleep Isn’t Better
It might seem like more sleep should equal better health, but research shows a U-shaped curve: both too little and too much sleep are linked with poor outcomes.
Sleeping more than 9–10 hours regularly has been associated with:
Shorter lifespan
Impaired cognition and risk of dementia
Higher rates of cardiovascular disease
Metabolic problems
Depression
It’s important to note that long sleep may be a symptom rather than a cause. For example, people with untreated sleep apnea, depression, or other chronic illnesses may be in bed longer because of underlying conditions, but are not actually getting high quality sleep that whole time. So, if you find yourself needing 9–10+ hours in bed and still feel unrefreshed, it’s worth checking in with your doctor.
The “Goldilocks Zone” for Sleep Duration
For most healthy adults, 7–9 hours per night is the sweet spot. The experts agree: The American Academy of Sleep Medicine (AASM) and the Sleep Research Society recommend at least 7 hours per night, and the National Sleep Foundation adds an upper limit, for 7-9 hours of sleep per night.
Important: the quality and regularity of your sleep matter, too. Fragmented or poor-quality sleep can leave you just as impaired as getting too few hours, as can frequent or rapid shifts in your sleeping schedule. “Social jetlag,” when people shift their sleep time later on weekends, also has negative impact on health.
Are there any exceptions? There are rare (perhaps 5%) of individuals who genetically need less or more sleep. They will usually have other family members with similar sleep patterns. Again, this is extremely rare, to the point I have never seen a patient with true short sleep duration, in 20 years of practice. So 90%+ of the time, if someone is sleeping regular hours and getting good quality sleep, their natural sleep need is 7-9 hours. People who fall outside of that range do exist but are rare. As much as we’d all like to be from one of these special short-sleeper superhuman families, if you need an alarm clock to wake up, you are not getting sufficient sleep or your sleep timing is off.
Key Takeaway
There’s no one-size-fits-all magic number, but the science is clear: Most adults thrive between 7 and 9 hours of sleep per night, with variations based on genetics, age, and health; outside of that range is linked to worse health and shorter lifespan. Still, 7-9 hours is a big range, so how do you know the right duration for you? For the answer, you will need to experiment a little and listen to your body.
Practical steps to find out how much sleep you need:
Track your natural rhythm. Notice how many hours you sleep on days without an alarm.
Set your wake time, prioritizing consistency. Then set your bedtime ahead by the number of hours you slept on days without alarm. If you skipped that step, start with 8 hours. Aim for a regular bedtime and wake time, even on weekends. At most, bedtime and wake time on weekdays should be an hour later than during work days.
Dial in: If you wake up feeling refreshed before your alarm consistently, that’s how much sleep you need. If you are still sleeping when your alarm goes off, move your bedtime earlier in 15-minute increments until you are consistently waking at the time of your alarm.
Check daytime functioning. If you feel alert, focused, and in a good mood, you’re in your optimal range!
If you’re getting 9+ hours of sleep at consistent hours, but you feel unrefreshed, tired, groggy, or sleepy during the daytime, this may be a symptom of something disrupting your sleep quality — you will want to get checked out for sleep disorders.
Overall, instead of chasing a rigid eight hours, or boasting about your four-hour nights, focus on setting up healthy consistent sleep habits and listening to your body.
