Sleep debt calculator
Add up the sleep you missed this week and see whether weekend lie ins make it back.
Your details
Most adults need 7 to 9 hours. If you wake refreshed after a week off, that is a good clue to your number.
A week of 6.5 h on weeknights, 8.5 h at weekends
6 h 30 min
short of the sleep you need, over a week
- Short on weeknights7 h 30 min
- Weekendpays back 1 h
- Average a night7 h 4 min
- NHS guide for most adults7 to 9 hours
- Social jetlagadd your usual wake up times to see it
Long weekend lie ins pay back only part of a short week and can shift your body clock. Going to bed a little earlier on weeknights, about 60 minutes, is usually the gentler fix.
See your GP if changing your sleep habits has not helped, you have had trouble sleeping for months, or it is making it hard to cope. If you feel sleepy while driving, stop somewhere safe.
The working
Need 8, get 6.5 on weeknights, 8.5 at weekends
Five weeknights at 1.5 hours short is 7.5 hours. Two weekend nights at half an hour extra pay back 1 hour, leaving 6.5 hours of sleep debt a week. The average night is 7 hours 4 minutes, inside the NHS 7 to 9 hour range but short of the 8 you need.
Paying it back
Steadier beats bigger
Long lie ins only pay back part of the debt and can shift your body clock, which makes Sunday night harder. Going to bed a little earlier on weeknights, even 30 to 60 minutes, is usually gentler than chasing it at the weekend.
Signs you need more
From the NHS
- Finding it hard to wake up or get going
- Feeling very tired, irritable or sleepy in the day
- Struggling to focus on everyday tasks
Social jetlag
When the weekend moves your body clock
Sleeping in shifts the middle of your sleep later, a bit like flying east and back every week. Researchers call it social jetlag (Wittmann and colleagues, 2006). Waking at 07:00 after 6.5 hours on weeknights puts the middle of your sleep at 03:45; waking at 09:30 after 8.5 hours at weekends puts it at 05:15, a shift of 1 h 30 min. Keeping weekend wake up times within about an hour of weekdays makes Monday mornings easier.
Read with care
What this cannot tell you
- Know your needEveryone is different; 7 to 9 hours suits most adults.
- Measure sleep qualityHours in bed are not the same as good sleep.
- Diagnose a sleep problemSnoring with pauses in breathing, or always being exhausted, needs a GP.
Questions
Common questions
Can you catch up on sleep at the weekend?
Partly. A bit of extra sleep helps, but long lie ins do not fully repay a short week and can make Monday harder.
How much sleep do adults need?
Most healthy adults need around 7 to 9 hours a night, according to the NHS.
Is sleep debt bad for you?
Regularly not getting enough sleep can affect mood, focus and energy, and over time your health. A steady routine is the best fix.
What about children and teenagers?
The NHS says children and teenagers usually need more sleep than adults, so this tool is set up for adults.
Sources
- Wittmann M et al. Social jetlag: misalignment of biological and social time. Chronobiol Int 2006
- NHS Every Mind Matters: sleep problems (7 to 9 hours; no caffeine 6 hours before bed)
- NHS: insomnia (sleep habits, and when to see a GP)
Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.
If you are always tired
See your GP if changing your sleep habits has not helped, you have had trouble sleeping for months, or tiredness is making it hard to cope. If you feel sleepy while driving, stop somewhere safe.