Chronotype, Social jetlag, Sleep irregularity

Sleep as Android watches your sleep pattern trends and can tell you your chronotype, social-jet-lag and sleep-irregularity.

1. Chronotype

Chronotype is a term used to characterise your sleep patterns. It is a spectrum ranging from 100% night owl to 100% morning lark.

Night owl

tends to stay up active until late night, usually past midnight, and wake up later. Wikipedia.

Morning lark

Named after a bird who rises very early in the morning. A human lark is a person who usually gets up early and feels most energetic towards the start of the day. They tend to get tired towards the evening. Wikipedia.

Note Your currently detected chronotype is always shown in the left menu if you have at least a month of sleep data.


You can also see your actual chronotype and chronotype trend in Charts.

1.1. Chronotype levels

We have divided the population into 10 groups (Morning Lark 5 to 1, Night Owl 1 to 5) according to their average mid sleep hour (the middle point between fall asleep hour and wake up hour. E.g. the mid-point between 10PM and 6AM would be 2AM).

Morning Lark 3 means that you tend to wake up in the morning (that’s the Morning lark part), and that your mid sleep hour is deviated from the population average less than 70% of population (i.e. you’re on the 30th percentile, or the second category from the center. That’s the '3' part).

chrono level
Figure 1. Chronotype, Owl / Lark level

If you were Morning lark 5, you would be a morning lark with the most mid sleep hour deviation from the average (10th percentile).

2. Social jet lag

Social jet lag is a term pioneered by Dr. Till Roenneberg in his book Internal Time. It describes a notion that when people have a completely free day, they will turn to their natural chronotype. But when they work a fixed schedule, they have to fight this natural tendency on workdays. This constant shifting of sleep pattern between workdays and weekend-days creates a certain tension that can be best compared to a periodic shifting of timezones – and a jet lag results.

chrono social jl
Figure 2. Social jetlag

Social jetlag as well as the other chronotype charts are part of the Charts screen on the Chronotype tab.

2.1. Workdays and weekend days

Sleep as Android does not actually use the usual definition of workdays and weekend-days, but compute „work-like days“ and „weekend-like days“ from your historical data there are such two obvious sleep pattern clusters in your data.

How do we do that? First, we cluster your data based on mid-sleep hour and sleep duration. Then we look for two sufficiently distinct clusters. If we find them, we consider the smaller one to be free days and the bigger one work days.

If we fail to find those two clusters, we base the distinction on the calendar using the common pattern, where Saturday and Sunday are the free days.

In Figure 3, “Weekdays vs. Weekends clustering” you see there is no obvious clustering for this users, as he sleeps regularly even on weekends.

chrono weekdays
Figure 3. Weekdays vs. Weekends clustering

3. Sleep irregularity

To get maximum of your sleep time, it is crucial to sleep regularly – go to sleep at the same time every day and sleep for a fixed period of time.

Sleep as Android tracks your sleep irregularity and shows you in Charts how irregular your sleep is.

The irregularity shown is the variance of your mid sleep hour.