Social jet lag: what it is and how to shrink it
Many people sleep later on weekends than on workdays. Researchers call the gap “social jet lag”: your body clock and your schedule run on different times, a bit like flying across time zones every weekend. You can work it out in two steps, and a few habits make it smaller.
What is social jet lag?
Social jet lag is the difference between the middle of your sleep on free days and on workdays (Roenneberg et al., 2019). If it is 2 hours 30 minutes later on free days, that is your social jet lag. A steady wake-up time and morning daylight keep the gap small.
Why is it called social jet lag?
Your body clock prefers certain sleep times; work and school set others. On workdays the alarm wins, on free days the body clock does. Researchers describe this gap between social and biological time as social jet lag (Wittmann et al., 2006).
How do you work out your social jet lag?
Take the middle of your sleep on free days and subtract the middle of your sleep on workdays (Roenneberg et al., 2019). The middle of sleep is halfway between falling asleep and waking up.
Example: workdays 11 pm to 7 am, middle 3 am. Free days 1 am to 10 am, middle 5:30 am. Difference: 2 hours 30 minutes. Use your usual times, not a single unusual weekend.
Across midnight, count the hours rather than the clock times: 11 pm to 7 am is 8 hours, so the middle lies 4 hours after 11 pm, at 3 am. The chronotype quiz does this arithmetic for you.
| Asleep | Awake | Middle of sleep | |
|---|---|---|---|
| Workdays | 11 pm | 7 am | 3 am |
| Free days | 1 am | 10 am | 5:30 am |
| Social jet lag | 2 hours 30 minutes |
Who has the most social jet lag?
Social jet lag is usually larger for later types (Roenneberg et al., 2019). Teenagers and young adults are on average later types than older adults (Fischer et al., 2017), so the gap is often largest at that age.
Why later types have more of it: early birds and night owls.
Does sleeping in on weekends help?
Sleeping in catches up on sleep that is missing during the week, which many later types do (Wittmann et al., 2006). At the same time it pushes the middle of your sleep later and makes the gap larger. Keeping your weekend wake-up time within about an hour of your weekday time is a common middle way.
What makes social jet lag smaller?
The same levers that move your body clock earlier: a steady wake-up time, daylight soon after waking and dimmer evenings (Brown et al., 2022). In a study with night owls, simple everyday 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).
Small steps of 15 to 30 minutes every few days are easier to keep up than a big jump.
Step by step: the 7-day plan to move your wake-up time earlier.
What this is not
Social jet lag is a measure of timing, not a medical assessment. Research on it mostly compares large groups, so there is no personal threshold you have to stay under. If you are tired for a long time no matter what you try, talk to a doctor.
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