Sleep Debt Calculator
Enter how much sleep you need and how long you slept each night to see how much sleep you're short this week, your average night and a gentle plan to catch up.
Adults are commonly advised to get at least 7 hours. This figure is commonly cited, not checked here; your own need may differ. Type 8, 7.5 or 7:30.
Type hours as 6.5 or 6:30. Leave a night empty to skip it.
Used with bed and wake times: taken off each night and counted before the middle of your sleep. 0 counts all your time in bed as sleep.
For example 30–60 minutes, by going to bed a little earlier. A simple arithmetic plan, not medical advice.
How your sleep debt is worked out
The sleep you needed, minus the sleep you got, over the nights you logged.
- 1
Add up your sleep
7 + 9 + 8.5 + 6.5 …= 50 h 30 min slept
- 2
Sleep you needed
8 h × 7 nights= 56 h needed
- 3
The gap is your debt
56 h − 50 h 30 min= 5 h 30 min debt
- 4
Your average night
50 h 30 min ÷ 7 nights= 7 h 13 min5 of 7 nights short
Read more: the formula, a worked example, social jet lag and notes
Sleep debt is the sleep you needed minus the sleep you got, added up over the nights you logged. Short nights add to it and longer nights take some off. The calculator also shows the shortfall on short nights alone, so a long weekend lie-in doesn't hide a run of short weeknights.
General information only, not medical advice. This is simple arithmetic on the numbers you enter. If you often feel very tired, struggle to fall or stay asleep, snore loudly, stop breathing in your sleep or have ongoing sleep problems, talk to a doctor.
The formula
Sleep needed = your sleep need a night × number of nights logged
Sleep debt = sleep needed − total sleep you got
Average a night = total sleep ÷ number of nights
Sleep from times = wake-up time − bedtime (add 24 hours if you woke the next day) − minutes to fall asleep
Nights to pay it back = sleep debt ÷ extra sleep a night, rounded up
Social jet lag = average middle of your sleep on weekend nights − the same on weekday nights
Worked example
You need 8 hours a night. Starting with last night, you slept 7, 9, 8.5, 6.5, 6, 6.5 and 7 hours. In total that is 7 + 9 + 8.5 + 6.5 + 6 + 6.5 + 7 = 50.5 hours. Over 7 nights you needed 8 × 7 = 56 hours, so your sleep debt is 56 − 50.5 = 5.5 hours (5 h 30 min).
Your average night is 50.5 ÷ 7 = 7.214 hours, about 7 h 13 min. Five nights were short (7, 6.5, 6, 6.5 and 7 hours), adding up to 1 + 1.5 + 2 + 1.5 + 1 = 7 hours short; the two longer nights (9 and 8.5 hours) gave back 1 + 0.5 = 1.5 hours, and 7 − 1.5 = 5.5 hours. With 30 extra minutes a night, paying back 5.5 hours takes 5.5 ÷ 0.5 = 11 nights; with 60 extra minutes it takes 5.5 ÷ 1 = 5.5, rounded up to 6 nights.
In Advanced, say last night was a Sunday with a Sat–Sun weekend, so the 9 and 8.5 hour nights were Saturday and Friday nights. The weekday nights average (7 + 6.5 + 6 + 6.5 + 7) ÷ 5 = 33 ÷ 5 = 6.6 hours (6 h 36 min) and the weekend nights (9 + 8.5) ÷ 2 = 8.75 hours (8 h 45 min). With the default bed and wake times, the middle of your sleep is 03:00, 03:00, 03:15, 03:30 and 03:15 on weekday nights (average 03:12) and 04:45 (00:30 to 09:00) and 05:30 (01:00 to 10:00) at the weekend (average 05:07:30). Your social jet lag is 05:07:30 − 03:12 = 1 h 55.5 min, which the calculator rounds to 1 h 56 min.
Sleep need by age
| Age | Recommended sleep in 24 hours |
|---|---|
| Newborn (0–3 months) | 14–17 h (incl. naps) |
| Baby (4–11 months) | 12–15 h (incl. naps) |
| Toddler (1–2 years) | 11–14 h (incl. naps) |
| Pre-school (3–5 years) | 10–13 h (incl. naps) |
| School age (6–13 years) | 9–11 h |
| Teenager (14–17 years) | 8–10 h |
| Young adult (18–25 years) | 7–9 h |
| Adult (26–64 years) | 7–9 h |
| Older adult (65+ years) | 7–8 h |
Ranges from the US National Sleep Foundation's recommendations (Hirshkowitz et al., 2015), as used on our sleep calculator. They are general guidance, not checked again for this page, and people's needs differ.
What social jet lag means
If you go to bed and get up much later on days off than on workdays, your body clock gets pulled back and forth each week, a bit like flying across time zones. Social jet lag measures that shift as the difference in the middle point of your sleep. A smaller number means a steadier routine. It is shown only when you enter bed and wake times and have both weekday and weekend nights in the log.
Notes
- Your need: set it to what leaves you feeling rested. The 8-hour default is only a starting point.
- Time in bed is not sleep: with bed and wake times, add the minutes it usually takes you to fall asleep for a closer figure. Waking in the night isn't counted.
- Paying it back: the payback plan is arithmetic only. Many people find small, regular extra sleep gentler than one very long lie-in, but catching up may not undo every effect of long-term short sleep.
- Your log stays on this device: the nights you type are kept in this browser for convenience and are not sent anywhere. A share link carries them in the link itself.
Common questions
What is sleep debt?
Sleep debt is the gap between the sleep you need and the sleep you actually get, added up over several nights. If you need 8 hours and sleep 6, that night adds 2 hours of debt. Over a week of short nights it can add up to many hours.
How do I work out my sleep debt?
Multiply your nightly sleep need by the number of nights, then take away the hours you actually slept. For example, needing 8 hours for 7 nights is 56 hours; if you slept 50.5 hours, your debt is 5.5 hours.
Can you pay back sleep debt?
Many people find that a little extra sleep over several nights, such as going to bed 30 to 60 minutes earlier, helps them feel better after a short week. One very long lie-in can shift your body clock and make the next night harder. Long-term sleep loss may not be fully undone by catching up, so steady sleep is the aim.
How much sleep do adults need?
Adults are commonly advised to get at least 7 hours a night, and many guides give a range of about 7 to 9 hours. This figure is commonly cited and has not been checked here. Your own need may differ, so this calculator lets you set it.
What is social jet lag?
Social jet lag is the shift in your sleep timing between workdays and days off. It is often measured as the difference in the middle point of your sleep: if you sleep 00:00 to 06:30 on weekdays (middle 03:15) and 01:00 to 10:00 at the weekend (middle 05:30), your social jet lag is 2 h 15 min, a bit like flying two time zones each weekend.
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Made by Zulu Calculator, part of AlphaZulu LLC. Formulas are shown in full and rule figures are checked against official sources; see how we build calculators.