Early bird or night owl? How chronotypes really work
Some people are wide awake at six in the morning, others only get going in the evening. Early bird and night owl are the everyday names for this; researchers call it your chronotype. The names sound like two camps, but they describe one scale, and part of where you sit on it can be shifted.
Are you an early bird or a night owl?
Early birds and night owls are the two ends of one scale, and most people sit somewhere in between (Roenneberg et al., 2007). Your place on that scale is your chronotype. Researchers often estimate it from the middle of your sleep on free days, with no alarm: asleep at 1 am and awake at 9 am gives 5 am.
One scale, not two camps
“Lark” and “owl” are colloquial words for people whose body clock runs earlier or later (Roenneberg et al., 2019). In large surveys, sleep times form a near bell-shaped curve. The most extreme early types wake up around the time the most extreme late types fall asleep, and most people are somewhere in between (Roenneberg et al., 2007).
Like many biological traits, chronotype varies continuously. That is why one widely used questionnaire, the Munich ChronoType Questionnaire (MCTQ), gives it as a clock time instead of sorting people into types, and any line between lark, owl and “in between” is drawn by convention (Roenneberg et al., 2019).
Early bird vs night owl: what actually differs
The difference is timing. The same clock time means something different to each body clock: researchers give the example that 8 am can correspond to 10 am on an early type’s body clock and to 6 am on a late type’s (Roenneberg et al., 2019).
That shows on workdays. Late types often cannot fall asleep early enough, the alarm cuts their night short, and they sleep longer on free days to catch up. Very early types have the opposite problem: social life keeps them up later than they would like, and they tend to sleep less on free days (Roenneberg et al., 2019).
The gap between workday and free-day sleep has its own name, social jet lag. It is usually larger for later types (Roenneberg et al., 2019).
How can you tell if you are an early bird or a night owl?
Look at your free days, with no alarm and no early plans. Note when you fall asleep and when you wake up, and take the time halfway between. Example: asleep at 1 am, awake at 9 am gives a midpoint of 5 am. This midpoint of sleep on free days is the measure behind the MCTQ (Roenneberg et al., 2007; Roenneberg et al., 2019).
Free days are used because your body clock is under less pressure to fit a schedule then. If you sleep much longer on free days to catch up, the midpoint moves later, so the MCTQ corrects for that catch-up sleep (Roenneberg et al., 2019).
Other questionnaires ask which times you would prefer. The MCTQ asks what you actually do, and the two approaches agree well (Roenneberg et al., 2019).
What makes someone an early bird or a night owl?
Researchers name three main factors: genes, light and age (Roenneberg et al., 2019).
Genes: a study of nearly 700,000 people found 351 genetic regions linked to being a morning person. The 5% of people carrying the most “morning” variants slept on average 25 minutes earlier than the 5% carrying the fewest (Jones et al., 2019). Even between these two extremes, the average difference was under half an hour.
Light: in an early survey, people who reported more time outdoors in daylight slept earlier, across all chronotypes (Roenneberg et al., 2003). Chronotypes are also earlier in rural areas than in cities (Roenneberg et al., 2019).
How do age and sex shift your chronotype?
In a US diary study with more than 50,000 people, chronotypes got later during the teenage years, were latest at around 19 and became earlier after that. Before 40, men were on average later types than women; after 40 it was the other way round (Fischer et al., 2017).
These are averages. Within every age group, chronotypes again formed a near bell-shaped curve (Fischer et al., 2017), so your own chronotype can sit well away from the average for your age.
Can a night owl become an early bird?
Partly, and light is the main lever. According to an international expert consensus, morning light can shift the body clock earlier and evening light can shift it later (Spitschan et al., 2025). When people lived with natural light only, on a summer camping trip, later types shifted the most and became more similar to earlier types (Wright et al., 2013).
In a study with night owls, simple daily rules (getting up earlier with morning light, fixed meal times, planned caffeine and exercise) moved sleep and wake times about two hours earlier over three weeks, without shorter sleep (Facer-Childs et al., 2019; Roenneberg et al., 2019).
The shift lasts as long as the habits do. Researchers point out that a late type drifts back to later times once the changes stop (Roenneberg et al., 2019). A 2026 policy brief recommends daylight especially within the first few hours after waking and dimmer light in the evening (Piper et al., 2026).
What this is not
Your chronotype describes when your body clock runs. The researchers behind the MCTQ see it as a biological timing rather than a psychological trait (Roenneberg et al., 2019). A quiz result is an estimate from your sleep times, not a measurement of your body clock. If you are tired for weeks no matter when you sleep, or your sleep times make everyday life hard, talk to a doctor.
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