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- Sleep debt = hours of sleep you needed − hours you actually slept.
- With a need of 8 hours and nights of 6, 6.5, 7, 5.5, 8, 9 and 6 hours, the debt over 7 nights is 8 hours.
- Long nights offset short ones in the main result. A second line counts only the short nights.
- The calculator shows how many nights of extra sleep it takes to repay the debt.
How to use the sleep debt calculator
Enter your sleep need
Type the hours you need per night. Most adults need 7 to 9.
Add your recent nights
List the hours you slept each night, for example the last 7 or 14 nights, separated by commas.
Read the debt
The main result is your sleep debt in hours, with your average sleep and how many nights fell short.
See the payback plan
Below, see how many nights it takes if you sleep 30 minutes, 1 hour or 2 hours extra each night.
How to calculate sleep debt
Add up the hours you needed over the period, add up the hours you slept, and subtract. If the result is positive, that is your sleep debt. A shorter night adds to the debt and a longer night pays some of it back.
Sleep debt formula
Hours needed = nightly need × number of nights
Sleep debt = hours needed − hours slept
Nights to repay = sleep debt ÷ extra hours slept per night
The shortfall line adds up only the nights where you slept less than you needed.
Worked examples
Need 8 hours, last 7 nights
Slept 6, 6.5, 7, 5.5, 8, 9 and 6 hours.
The 9-hour night offsets 1 hour, which is why the debt is 8 and not 9.
Paying back 8 hours
Extra sleep each night.
These are simple sums. In real life recovery is gradual.
Where a sleep debt calculator helps
Busy weeks
See how much sleep you lost over a hard week.
Students
Check your average during exams.
Shift workers
Track the effect of changing shifts.
Plan ahead
Find your need first with the sleep calculator.
Sleeping in once does not always erase several short nights, and recovery can take days. Aim for steady, regular sleep. If you are always tired even with enough sleep, or snore loudly or stop breathing at night, talk to a doctor.
Sleep debt calculator FAQ
What is sleep debt?
Sleep debt is the gap between the sleep you need and the sleep you get over a period of time.
How do I calculate sleep debt?
Multiply your nightly need by the number of nights, add up the hours you slept, and subtract.
Can you catch up on sleep at the weekend?
A long lie-in can help a little, but it may not fully make up for a week of short nights. Regular sleep each night is better.
How long does it take to recover?
It depends on how large the debt is. Sleeping an hour extra each night would take about as many nights as the hours of debt.
How many hours should I count as my need?
Most adults need 7 to 9 hours. If you wake up rested without an alarm after a few relaxed days, that number is a good guide.
Why does the debt ignore a long night?
The main result lets long nights offset short ones. The shortfall line shows the total of only the nights that fell short.