See how much sleep you've actually missed this week, and what it would take to catch up.
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Sleep debt builds up quietly, an hour missed here, thirty minutes there, until it adds up to something that genuinely affects how you feel and function. This calculator puts a real number on it.
Sleep debt is the cumulative difference between the sleep your body needs and the sleep it actually gets. Miss an hour a night for a week, and you have accumulated 7 hours of debt, roughly a full night's sleep behind.
Partially. Sleeping in on weekends or adding an extra hour a night for a few days can repay short-term debt and improve alertness. However, research suggests chronic, long-term sleep debt has effects that are not fully reversed by a single recovery period, consistency matters more than occasional catch-up sleep.
Once you know your debt, our Sleep Cycle Calculator can help you time your next few nights to recover more effectively, and our Heart Rate Zones tool in Heart Health is worth checking too, since poor sleep and overtraining often compound each other.
There is no strict cutoff, but consistently carrying more than 5-10 hours of weekly debt is generally associated with noticeable daytime impairment.
Both have tradeoffs, sleeping in can repay some debt, but wildly inconsistent schedules can disrupt your circadian rhythm. Small, consistent extra sleep tends to work better than one big catch-up night.
Somewhat, a short nap can reduce sleepiness and partially offset debt, though it is not a full substitute for nighttime sleep. See our Nap Calculator for how to time one well.