Social Jetlag Calculator

Sleeping in on weekends shifts your body clock a bit like crossing time zones. Enter your usual weekday and weekend sleep times to see how far it moves.

Your Social Jetlag (Mid-Sleep Shift)

2h 15m

Large shift (2 h+)

It's a bit like flying 2 time zones west on Friday and back east on Sunday night, which is why Monday feels rough.

Mid-sleep: 2:45 AM weekdays, 5:00 AM weekends. Wake time moves 3h later.

Notice drift before Monday does

ARC compares your median wake time over the last two weeks with the two weeks before, so one late Saturday isn't read as a trend. When your schedule is drifting later, it tells you, and its 20-minute morning light timer on your Lock Screen is the simplest way to pull it back.

Download on theApp Store

How This Calculator Measures Social Jetlag

Social jetlag is the gap between your body's preferred timing and the schedule your week imposes. For the full explanation, read what social jetlag is and why Mondays hurt. This calculator uses the measure researchers use: the difference between the midpoint of your sleep on weekends and on weekdays (Wittmann, Dinich, Merrow & Roenneberg, 2006).

Say you sleep 11 PM to 6:30 AM on weekdays, then 12:30 AM to 9:30 AM on Saturday and Sunday. Your mid-sleep moves from 2:45 AM to 5:00 AM, a shift of 2 h 15 min. It's a bit like flying from New York to Los Angeles on Friday and back on Sunday: your clock gets pulled later, then dragged back.

Why does it matter?

Your body clock doesn't know what a weekend is. It takes its cues from light, above all morning light. When you sleep in and see your first daylight hours later, your clock drifts later too, so your melatonin rises later on Sunday evening. That's why it's hard to fall asleep on Sunday night, and why Monday feels rough.

Studies link larger social jetlag with higher BMI in some groups (Roenneberg et al. 2012, Current Biology) and a higher resting heart rate (Rutters et al. 2014, Journal of Biological Rhythms). These are associations; how much social jetlag itself causes is still being worked out.

A Useful Target: Within About an Hour

Consistency matters more than any single night. A practical target is to keep your weekend wake time within about 60 minutes of your weekday one. If you do sleep in, get about 20 minutes of outdoor light soon after waking to help anchor your rhythm.

Frequently asked questions

How is social jetlag calculated?

Researchers compare the midpoint of your sleep on free days with the midpoint on work days (Wittmann and colleagues, 2006). If you sleep 11 PM to 6:30 AM on weekdays and 12:30 AM to 9:30 AM at weekends, your mid-sleep moves from 2:45 AM to 5:00 AM: 2 h 15 min of social jetlag.

How much social jetlag is too much?

There's no official cutoff. Under an hour is small; many researchers treat two hours or more as large. Studies link larger social jetlag with higher BMI in some groups and a higher resting heart rate, but those are associations, and the size of the effect varies.

Is sleeping in on weekends bad?

Not in itself. If you're short on sleep, the extra rest helps. The catch is that a much later wake time also shifts your body clock later, which makes Sunday night harder to fall asleep and Monday morning harder to wake up.

How do I reduce social jetlag?

Keep your weekend wake time within about an hour of your weekday one, go to bed a little earlier on weekdays if you're short on sleep, and get about 20 minutes of outdoor light soon after waking, especially on weekend mornings.

Related reading