What this calculator works out
This calculator adds up seven nights of sleep, compares the total against your target, and reports the average, the accumulated shortfall and a rough estimate of how many nights of recovery it would take.
Sleep debt accumulates quietly. An hour short each night feels manageable in isolation and amounts to a full night's sleep missing by the end of the week.
Sleep this week
Enter sleep achieved for the last 7 nights.
Before you fill it in
- Enter time actually asleep, not time in bed. Most people are awake for 20 to 40 minutes of a night without remembering it.
- Leave the target blank to use an age-based default: 9 hours under 18, 7.5 hours over 64, 8 hours otherwise.
- Use a normal week rather than one containing a night shift or a late event, unless that is your normal.
- Estimates are fine. The pattern across seven nights matters more than precision on any one.
You cannot repay several hours of lost sleep in one long lie-in. Recovery sleep is more efficient than normal sleep but limited in how much extra can be taken per night, which is why the estimate here allows only about 45 minutes of recovery a night and why a week of short nights takes more than a weekend to clear.
How this calculator works
A weekly total against a weekly target:
Total = sum of the seven nights
Ideal = target × 7
Sleep debt = ideal − total, never below zero
Average = total ÷ 7
Recovery nights ≈ debt ÷ 0.75The recovery figure assumes about 45 minutes of additional sleep per night is achievable, which is a conservative and realistic rate for most people.
The status bands are under 2 hours well balanced, 2 to 7 hours moderate, and above 7 hours high. These are rules of thumb rather than clinical thresholds.
Worked example: seven hours a night
Using the default figures — an 8 hour target with seven nights of 7 hours each:
- Total: 49 hours against an ideal of 56
- Average: 7 hours a night
- Sleep debt: 7 hours — a full night missing
- Recovery estimate: 10 nights
One hour short a night never feels like a problem on any given day, and produces an entire missing night by Sunday. The recovery figure is the uncomfortable part: ten nights of sleeping 45 minutes longer, which in practice means the debt is usually still there when the next week starts adding to it.
Common mistakes
- Entering time in bed rather than time asleep. The difference is typically 20 to 40 minutes a night.
- Assuming a weekend lie-in clears the week. Recovery is limited to roughly 45 minutes a night.
- Choosing an unrepresentative week. Use a normal one.
- Treating a low debt as proof of good sleep. Quality matters as much as quantity.
- Setting the target from what you manage rather than what you need.
Frequently asked questions
Can I catch up at the weekend?
Partially. Extra weekend sleep reduces sleepiness and helps, but studies have found it does not fully reverse the metabolic and cognitive effects of a week of restriction. Irregular timing — very late nights and long lie-ins — also shifts your body clock, which can make the following Monday harder.
What are the effects of sleep debt?
Reduced concentration and reaction time, impaired mood and decision-making, greater appetite and reduced glucose tolerance in the short term. Sustained short sleep is associated with higher risk of cardiovascular disease, type 2 diabetes and depression. Driving while sleep deprived carries risks comparable to some levels of alcohol impairment.
How do I know if I am getting enough?
Waking without an alarm feeling rested, and not feeling sleepy during the day, are the practical indicators. Needing an alarm every day, falling asleep within a couple of minutes of lying down, or feeling drowsy in the early afternoon most days all suggest insufficient sleep.
When should I see a GP?
If poor sleep persists for more than a few weeks and affects your daily life, or if you snore heavily and wake unrefreshed, which can indicate sleep apnoea. NHS talking therapies offer cognitive behavioural therapy for insomnia, which has stronger long-term evidence than medication and can often be accessed by self-referral.
Is what I enter stored?
No. Your sleep figures are processed in your browser and never transmitted or retained.
Related tools
References
- NHS — sleep guidance, insomnia advice and sleep apnoea information
- National Institute for Health and Care Excellence — guidance on insomnia management
Sources are checked at publication and can change — how I choose and check references.