How to Calculate Sleep Debt

Sleep debt = (hours needed per night × nights) − hours actually slept. Needing 8 hours and sleeping 6, 6, 7, 8, 5, 9 and 6 hours over seven nights gives 56 − 47 = 9 hours of debt, an average of 6.714 hours (need 8) and 5 of 7 nights short of target. The sleep debt calculator does this from a list of nights.

These are ranges, not targets for everyone. Your own need within the range is the figure to use in the calculation.

Partly. Sleeping longer for several nights improves how people feel and perform, but research suggests a single long night or a weekend lie-in does not fully reverse a week of short sleep, and big swings in sleep timing have costs of their own. Treat the “nights to repay” figure as a rough guide: adding 30–60 minutes a night for a couple of weeks is more realistic and sustainable than trying to repay it all at once.

• Keep a regular bedtime and wake time, including weekends.
• Add 30–60 minutes of sleep per night rather than one marathon night.
• Cut caffeine early — see how much is left at bedtime with the caffeine calculator.
• Dim lights and screens in the hour before bed; keep the bedroom cool and dark.
• Avoid heavy meals and alcohol close to bedtime.

If you sleep enough but still feel exhausted, snore loudly, stop breathing at night, or struggle to sleep regardless of effort, talk to a doctor — conditions such as sleep apnoea and insomnia are common and treatable. This guide is general information, not medical advice.