Sleep Debt Calculator
Add up how much sleep you're missing compared with what you need, and how long it takes to catch up.
About the Sleep Debt Calculator
Enter how much sleep you need and the hours you actually slept on each of the last seven nights. The calculator adds up the shortfall (or surplus), gives your average per night and estimates how many nights it takes to catch up with an extra hour a night.
Sleep debt is the running total of sleep you needed but didn't get. Most adults need 7–9 hours. Short-term debt can be repaid by sleeping a little longer for several nights; a long lie-in at the weekend only partly helps and can shift your body clock.
The formula
Sleep debt = Σ (need − hours slept)
Worked example
Needing 8 h; slept 6.5, 7, 6, 5.5, 7, 9 and 8.5 h
- Shortfalls: 1.5 + 1 + 2 + 2.5 + 1 − 1 − 0.5 = 6.5 h
- Average 7.07 h a night
- An extra hour a night clears it in about 7 nights
Things to keep in mind
- Counts hours only, not sleep quality. Snoring, waking often or feeling unrefreshed despite enough hours is worth discussing with a doctor.
Questions people ask
Can I really catch up on sleep?
Short-term debt, yes, over several nights. Chronic shortfalls are better fixed with a regular, earlier bedtime.
How do I know how much I need?
On holiday, with no alarm, the amount you settle into after a few days is a good guide.
Do naps count?
Yes, add them to that day's hours. Keep naps short and before mid-afternoon so they don't spoil the night.