Morning Person or Night Owl? The Science of Chronotypes
Your body clock is partly genetic, shifts with age and is set by light. Chronotypes, why teens sleep late, what social jet lag does, and how to work with yours.
Some people bound out of bed at six, clear-headed and cheerful. Others hit snooze three times, can’t form a sentence before ten, and do their best work at midnight. It’s tempting to see this as a matter of discipline: the early birds are organised, the night owls lazy.
Biology disagrees. Your sense of when you’re sharp and when you’re flagging is set by a clock in your brain, and that clock doesn’t run on the same time for everyone. The timing of yours is called your chronotype. Slide the toy at the top to see how the same working day lands differently on an early clock and a late one.
Try it
Your day, by your body clock
Set how early or late your clock runs, and when your day has to start.
For a night owl, the body would naturally wake around 09:30. Starting at 07:00, alertness is about 7% of its peak, 2.5 hours before your body is ready: that gap, every weekday, is social jet lag.
Your body clock
Almost every cell in your body runs on a roughly 24-hour cycle, called a circadian rhythm, from the Latin for “about a day”. A master clock, a cluster of around 20,000 nerve cells in the brain called the suprachiasmatic nucleus, sits just above where the optic nerves cross, and keeps the rest in step. It times when you feel sleepy, when your body temperature peaks and dips, when hormones like melatonin rise in the evening and cortisol in the morning.
Your chronotype is where your personal clock sits relative to the day: early (a morning lark), late (a night owl), or, for most people, somewhere in between. Researchers measure it with questionnaires about when you’d naturally sleep and feel alert, such as the Horne–Östberg Morningness–Eveningness Questionnaire, and by tracking when people sleep on days with no alarm. On a free day, the midpoint of your sleep is a good, simple measure.
What sets it
Genes. Chronotype is partly inherited. A 2019 study of nearly 700,000 people found more than 350 places in the genome linked to being a morning or evening person. A few rare gene variants can shift a person’s clock by hours, so that whole families fall asleep at 7.30 pm and wake at 3 am.
Age. Chronotype changes predictably across life. Children tend to be early risers. During adolescence, the clock shifts later, and keeps shifting until it reaches its latest point around 19 to 21, a little earlier for women than men. It’s so regular that Till Roenneberg and colleagues proposed it as a biological marker of the end of adolescence. From there, most people drift earlier again for the rest of their lives, which is why grandparents are up at dawn.
Light. Light is the strongest signal that sets the clock each day. Morning daylight pulls it earlier; bright light late in the evening, including from screens and indoor lighting, pushes it later. Indoor light is dim compared with daylight, even on a cloudy day, so people who spend their days indoors and their evenings under bright lights drift later than their genes alone would put them.
Try it
A week in a tent
In a 2013 study, people spent a week camping in the Rocky Mountains with no electric light at all, only sunlight and campfires. What happened to their body clocks?
Pick one. You’ll see why straight after.
Social jet lag
Problems arise when your body clock and your schedule disagree. An owl with an 8 am start is effectively living in a different time zone on weekdays, then catches up with long lie-ins at weekends. Roenneberg called this social jet lag.
Try it
How common is social jet lag?
Social jet lag is the gap between when your body would like to sleep and when your schedule makes you sleep, shown by sleeping later on free days. In a large European survey, what share of people had at least an hour of it?
Drag the dot to your guess, then lock it in. Nothing is revealed until you do.
Like real jet lag, it leaves people tired, irritable and less sharp. Larger social jet lag has been linked with more smoking, more alcohol and a higher body weight, though these studies show associations, and the causes run in more than one direction.
The teenage problem
The mismatch is worst for teenagers, whose clocks run latest just when schools ask them to be up earliest. A sixteen-year-old forced to wake at 6.30 am is, by their own body clock, being woken in the middle of the night.
This is why many sleep researchers, and the American Academy of Pediatrics, have argued for later school start times for teenagers. When schools in Seattle moved their high school start from 7.50 to 8.45 am in 2016, a study found students slept about half an hour more a night, and their grades and attendance improved. It’s a rare example of a change in schedule shifting the outcome without any change in effort.
Is one better than the other?
Neither chronotype is better in itself. Morning types tend to fit more easily into a world of early starts, which may explain some of the advantages sometimes reported for them, such as slightly better school marks. Evening types aren’t less able. When people are tested at their own peak times, performance differences shrink, and in some studies evening types do better on tasks that involve creativity or flexible thinking.
Some large studies have linked a strong evening chronotype with higher rates of depression and some health problems. Much of that may come from the constant mismatch with schedules, not from being an owl as such. The lesson isn’t that owls should feel bad. It’s that the mismatch is costly, and worth reducing where you can.
Working with your clock
Find your peak. Most people have a window of a few hours when they’re sharpest. For larks it’s the morning; for owls, afternoon or evening; for the in-betweens, often late morning. Notice when you do your best thinking over a week or two.
Put hard things in your peak. Save demanding thinking, studying and decisions for then, and routine tasks for your off-peak hours. Psychologists call it the synchrony effect: on demanding mental tasks, people perform better at their preferred time of day.
Use light deliberately. If you want to shift earlier, get daylight soon after waking, ideally outside, and dim the lights and screens for the last hour or two before bed. Shifts are modest, perhaps an hour or so, but real.
Keep wake times steady. Big differences between weekday and weekend wake times are the engine of social jet lag. A lie-in of an hour helps; a lie-in of four can leave you jet-lagged on Monday.
Respect the post-lunch dip. Almost everyone has a mild slump in alertness in the early afternoon, whatever their chronotype. It’s a natural part of the cycle, not a sign of a heavy lunch alone.
If you can, negotiate your schedule. Flexible start times, later meetings for owls and earlier ones for larks, put people’s best hours to work instead of wasting them.
Measure your own clock in a fortnight
You don’t need a lab. For two weeks, write down when you fall asleep and when you wake on days when no alarm or child wakes you. Work out the midpoint of each night’s sleep: someone who sleeps from midnight to 8 am has a midpoint of 4 am. Average the midpoints of your free days.
That number is a good estimate of your chronotype. A midpoint around 3 am is early; around 4 am is typical for adults; 5 am or later is a clear night owl, and teenagers often sit at 6 am or beyond. Now do the same for your work or school days. The difference between the two is your social jet lag.
It’s worth also noting the hours when you feel sharpest, and when you crash. Most people find the pattern is steadier than they expected, which makes it much easier to plan around. It also tends to surprise people in one direction: most of us are later than our alarms suggest.
What it doesn’t mean
Being a night owl isn’t an excuse for short sleep, and being a lark doesn’t make you virtuous. Both need enough sleep, typically seven to nine hours for adults. Your chronotype decides when that sleep comes most easily. And if you have serious, persistent trouble sleeping or staying awake, that’s worth talking to a doctor about: it may be more than a chronotype.
Find your chronotype
The free chronotype test has 24 quick statements and places you between night owl and morning lark, with advice on planning around your peak. The study myths test covers how sleep and timing affect learning.
Questions people ask
- What is a chronotype?
- Your natural timing for sleep and alertness: whether your body clock runs early, like a morning lark, late, like a night owl, or somewhere in between, which is where most people are. It shows up in when you’d naturally fall asleep and wake if nothing set an alarm.
- Can you change your chronotype?
- Partly. Genes and age set a baseline, but light shifts the clock day to day. Bright daylight soon after waking, dim lights and screens in the evening, and steady wake times can move you earlier by an hour or more. A full owl rarely becomes a full lark.
- Why do teenagers sleep so late?
- Their body clocks shift later during adolescence, peaking around 19 to 21, so they genuinely find it hard to fall asleep early. It’s biology, not just laziness. It’s why many sleep researchers support later school start times for teenagers.
- What is social jet lag?
- The mismatch between your body clock and your social schedule, often measured as how much later you sleep on free days than on work or school days. A two-hour gap is like flying two time zones every weekend. About two thirds of people have at least an hour.
- Are morning people more successful?
- Morning types fit more easily into a world of early starts, which may explain some advantages reported for them at school and work. Evening types aren’t less able: tested at their own peak times, the differences shrink. The problem is the mismatch, not the type.
Sources and further reading
- Roenneberg, T., Kuehnle, T., Pramstaller, P. P. et al. (2004). A marker for the end of adolescence. Current Biology, 14(24), R1038–R1039.
- Wittmann, M., Dinich, J., Merrow, M. and Roenneberg, T. (2006). Social jetlag: Misalignment of biological and social time. Chronobiology International, 23(1–2), 497–509.
- Roenneberg, T., Allebrandt, K. V., Merrow, M. and Vetter, C. (2012). Social jetlag and obesity. Current Biology, 22(10), 939–943.
- Wright, K. P. et al. (2013). Entrainment of the human circadian clock to the natural light-dark cycle. Current Biology, 23(16), 1554–1558.
- Jones, S. E. et al. (2019). Genome-wide association analyses of chronotype in 697,828 individuals. Nature Communications, 10, 343.
- Dunster, G. P. et al. (2018). Sleepmore in Seattle: Later school start times are associated with more sleep and better performance in high school students. Science Advances, 4(12), eaau6200.
