Find Your Chronotype: Early Bird, Night Owl or In Between?
Your chronotype describes when your body wants to sleep when no alarm gets in the way. The calculator works it out with the same formula Circadian applies to your sleep data: from the midpoint of your sleep on free days, corrected for catch-up sleep.
On workdays
On free days, without an alarm
The calculator applies the formula from chronobiology to your answers. It does not replace a validated questionnaire or a diagnosis.
How research measures chronotype
Chronobiologists around Till Roenneberg in Munich developed a questionnaire for this, the Munich ChronoType Questionnaire. It asks about sleep times on workdays and free days separately. [1] More than 55,000 people have completed it. [2]
What counts is the midpoint of sleep on free days, when no alarm interferes. One correction is added: if you sleep too little during the week, you sleep longer at the weekend and therefore seemingly later. The midpoint is therefore moved earlier by half of the catch-up sleep. [2] In the literature the result is called MSFsc.
Worked example: Someone sleeps from 23:30 to 6:30 on five workdays, seven hours, and from 1:00 to 10:00 at the weekend, nine hours. The midpoint of sleep at the weekend is 5:30. On average across the week the person sleeps 7.6 hours, so 1.4 hours more at the weekend. Half of that, 43 minutes, is subtracted: the corrected midpoint is 4:47. That is a normal type, just short of a night owl. The calculator above starts with these values.
What your result means
Circadian sorts it like this: if the corrected midpoint is before 3:00, you are an early bird; after 5:00, a night owl; in between, a normal type. The boundaries are a classification for the app, not a diagnosis. In reality, chronotype is a continuous spectrum: sleep times in a population are roughly normally distributed, and extreme early types wake up when extreme late types fall asleep. [2]
Chronotype also depends on age. Children are usually early, teenagers become later and later, and people are latest around the age of 20. After that, chronotype becomes earlier again. [3]
What Circadian does with your chronotype
In Circadian, your chronotype shifts your whole energy curve: an hour and a half earlier for early birds and an hour and a half later for night owls. Highs and lows then come correspondingly earlier or later.
If you share Apple Health data, the app suggests your chronotype from the sleep data of the last six weeks. It only does so once at least four free days have been recorded; with less data, your own setting stays in place. Because a sleep midpoint can fall just before or just after midnight, the app averages clock times as on a clock face rather than as plain numbers. Otherwise the average of 23:50 and 0:10 would come out as 12 noon.
When everyday life and chronotype don’t match
Night owls are hit hardest by the alarm clock: during the week they build up sleep debt and catch up several hours at the weekend. [1] The gap between the midpoints of sleep on workdays and on free days is called social jetlag. [4] The calculator shows it too; what it means is explained in the article on social jetlag.
Can you shift your chronotype?
Partly. Genes and environment together determine where you sit on the spectrum. [4] The most important cue from the environment is light: people who spend more time outdoors in daylight sleep earlier. [1] Bright light in the morning moves the body clock earlier; light in the evening moves it later. [5]
Sources
- Roenneberg T, Wirz-Justice A, Merrow M (2003). Life between clocks: daily temporal patterns of human chronotypes. Journal of Biological Rhythms 18(1):80–90.
- Roenneberg T, Kuehnle T, Juda M, Kantermann T, Allebrandt K, Gordijn M, Merrow M (2007). Epidemiology of the human circadian clock. Sleep Medicine Reviews 11(6):429–438.
- Roenneberg T, Kuehnle T, Pramstaller PP, Ricken J, Havel M, Guth A, Merrow M (2004). A marker for the end of adolescence. Current Biology 14(24):R1038–R1039.
- Wittmann M, Dinich J, Merrow M, Roenneberg T (2006). Social jetlag: misalignment of biological and social time. Chronobiology International 23(1–2):497–509.
- Khalsa SBS, Jewett ME, Cajochen C, Czeisler CA (2003). A phase response curve to single bright light pulses in human subjects. Journal of Physiology 549(3):945–952.
This article is for general information only and does not replace medical advice. Consult your doctor for health-related questions.
A chronotype suggestion from your sleep data
Circadian suggests your chronotype from your Apple Health sleep data and aligns your energy curve with it.
- Chronotype suggestion from six weeks of sleep data
- Sleep review over 14 or 30 days, night by night
- Energy curve from sleep and other Health data
- One-time purchase, no subscription and no account; analysis happens only on your devices
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