Social jetlag is the gap between when you sleep on free days and when you sleep on work days — measured as the difference in your mid-sleep time. Sleeping and waking much later at the weekend drags your body clock around like a short-haul flight across time zones, and the bill often arrives on Monday.
The cleanest way to measure it is mid-sleep: the clock time halfway between falling asleep and waking. If your mid-sleep on a work night sits at 03:30 but drifts to 06:00 at the weekend, that two-and-a-half-hour gap is your social jetlag. It captures something total sleep hours miss — not how much you slept, but when — and the “when” is what your internal clock cares about most.
When you stay up and sleep in on Saturday and Sunday, your body clock shifts later, just as it would if you'd flown west. Then Monday's alarm yanks it back east before it has adjusted. You're awake and commuting while your physiology still thinks it's the small hours — groggy, low on appetite, slow to warm up. No plane was involved, but the desynchrony is the same.
The shift doesn't undo itself overnight. A clock that drifted two hours later over a weekend needs several days of earlier mornings to settle, so the start of the week is when the mismatch is widest. That's part of why Monday so reliably feels harder than its sleep total alone would predict — you're not just tired, you're misaligned.
Larger, repeated social jetlag has been associated in research with worse mood, poorer metabolic markers and a tendency to feel more tired across the following week — though it tends to travel alongside late chronotypes and short sleep, so the threads are hard to fully separate. None of this is a diagnosis; it's a pattern worth noticing rather than a verdict on your health.
The lever that moves social jetlag most is wake time, not bedtime. Keeping your alarm within roughly an hour of its weekday setting — even at the weekend — stops the clock from drifting in the first place, which beats trying to drag it back every Monday. If you're short on sleep, a modest lie-in or a short early-afternoon nap recovers some of it without shoving your whole rhythm later.
Vitra's Circadian view computes your social jetlag for you — comparing your mid-sleep on free days against work days from your Oura sleep timing — and surfaces a plain-language note when the gap runs high, all worked out locally on your machine against your own pattern rather than a generic rule.
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