Habits
Social Jet Lag Calculator
Social jet lag, a term from chronobiologist Till Roenneberg and colleagues, is the difference between the timing of your sleep on workdays and on free days. Going to bed and waking much later on weekends is a bit like flying a few time zones west every Friday and back every Monday. It is measured as the gap between the midpoints of your sleep. The midpoint on free days is also a rough marker of your chronotype.
How it works
Sleep midpoint = sleep onset + half the sleep duration. Social jet lag = the absolute difference between the free day midpoint and the workday midpoint, taking the shorter way around the clock.
Example
Workdays 11:00 PM to 6:30 AM: 7.5 h, midpoint 2:45 AM. Free days 12:30 AM to 9:30 AM: 9 h, midpoint 5:00 AM. Social jet lag = 2 h 15 min.
Assumptions and limits
- This is the simple version of the measure; the research version adds a correction for oversleeping on free days to repay sleep debt.
- The summary bands are descriptive, not clinical categories.
- Large social jet lag often means you are not getting enough sleep on workdays.
Frequently asked questions
Why does social jet lag matter?
Studies have linked larger social jet lag with poorer mood, more sleepiness, and higher body weight, although these are associations and do not prove cause. A regular sleep schedule is a core part of healthy sleep advice.
How do I reduce social jet lag?
Keep wake time within about an hour on free days, get morning light, and move workday bedtime earlier if you are short on sleep during the week.
What does my free day midpoint say about my chronotype?
A later midpoint on free days suggests a later chronotype (night owl). Chronotype shifts later in adolescence and earlier again with age.
Sources
Tools and screening scores are general information. They cannot diagnose or rule out a sleep disorder. Read our medical disclaimer.