Find your best bedtime or wake-up time
A sleep calculator works out the best bedtime or wake-up time by counting backwards or forwards in complete 90-minute sleep cycles, rather than a fixed number of hours. Enter a wake-up time or a bedtime below, and you'll get several options — each one ending at the natural break between cycles, so you wake up during light sleep instead of deep or REM sleep.
We assume it takes about 14 minutes to fall asleep, then count backwards in full 90-minute cycles.
Recommended bedtimes
Most adults need 5 to 6 complete sleep cycles a night — that's why 7.5 hours (5 cycles) often feels more refreshing than 8 hours, which ends mid-cycle. Scroll down to see how sleep cycles work, how much sleep you need by age, and how to recover from sleep debt.
How it works
Choose your target time
Tell the calculator either when you plan to wake up or when you plan to go to sleep.
We calculate in full 90-minute cycles
Each sleep cycle lasts around 90 minutes and moves through light sleep, deep sleep and REM sleep. Waking up mid-cycle is what causes that groggy feeling. This calculator lands you between cycles instead.
Get several optimal time options
You'll see a few options — for example, 5 cycles = 7.5 hours, 6 cycles = 9 hours — so you can pick whichever fits your schedule.
What is a sleep cycle?
A sleep cycle is a repeating ~90-minute pattern the body moves through several times a night, progressing through four stages: light sleep (NREM Stage 1), core sleep (NREM Stage 2), deep sleep (NREM Stage 3), and REM sleep — before starting again.
The transition into sleep. Muscles relax, heart rate slows, and you can be woken easily.
Body temperature drops and heart rate continues to slow. This stage makes up the largest share of total sleep time.
The most physically restorative stage — important for muscle repair, immune function, and is hardest to wake from.
Rapid Eye Movement sleep, when most dreaming happens — important for memory consolidation and mood regulation.
A typical night's sleep cycle pattern
The chart below shows how sleep stages typically shift across a night: deep sleep dominates the early cycles, while REM sleep periods get longer as the night goes on — which is why waking naturally near the end of a cycle, closer to light sleep, feels easier than being woken from deep sleep.
Illustrative hypnogram: deep sleep is concentrated in early cycles; REM periods lengthen closer to morning.
Each cycle lasts roughly 90 minutes, though it can range from 80 to 120 minutes depending on the person and the night. This is the whole reason a sleep calculator is more useful than simply picking "8 hours" of sleep — it works out a time that lands you in light sleep, not deep or REM sleep, when your alarm goes off.
↑ Try the calculator aboveHow much sleep do you need?
Most healthy adults need around 7 to 9 hours of sleep a night, according to NHS guidance — but the right amount depends heavily on age, with babies, children and teenagers all needing more than adults.
| Age group | General sleep guidance |
|---|---|
| Newborns (0–3 months) | 8–16 hours |
| Infants & toddlers (4 months–2 years) | 11–15 hours |
| Preschoolers (3–6 years) | 10–12 hours |
| School-age children (7–12 years) | 10–11 hours |
| Teenagers (13–18 years) | 8–10 hours |
| Adults (18–64 years) | 7–9 hours |
| Older adults (65+) | 7–8 hours |
General guidance based on NHS sleep advice and widely used paediatric sleep guidelines. Individual needs vary — a GP or health visitor can give guidance specific to a child's development.
Working out sleep for children? Use the tool above in the same way — enter their usual wake-up time (for example, for school) and the calculator will suggest an appropriate bedtime based on full sleep cycles.
↑ Calculate your child's sleep scheduleWhat is sleep debt?
Sleep debt is the cumulative gap between the sleep you actually get and the sleep your body needs. It builds up gradually: losing just 60 minutes a night for a week adds up to a full night's sleep owed back to your body.
How to recover from sleep debt
Recovery works best gradually rather than with one long catch-up sleep. Going to bed 30–60 minutes earlier over several nights, staying consistent with sleep and wake times, and prioritising a full night's sleep when you can, all help pay down sleep debt without disrupting your circadian rhythm further.
Can you fully catch up on lost sleep?
Partially, but not perfectly. A single long lie-in can ease short-term tiredness, but it doesn't fully reverse the effects of chronic sleep loss the way consistent, adequate sleep does — which is why prevention (using the calculator to plan realistic bedtimes) works better than repeated catch-up sleep.
↑ Use the calculator to plan your recoverySleep calculator UK — NHS guidance & local context
The NHS advises that most healthy adults need around 7 to 9 hours of sleep, though this varies with age, health and personal circumstances — this calculator combines that guidance with the 90-minute sleep cycle method to suggest specific times, not just a total number of hours.
Poor sleep is common in the UK — NHS resources note that a large proportion of adults report ongoing difficulty sleeping well. Most short-term sleep problems settle within about a month; if sleep difficulties persist longer than that, the NHS recommends speaking to a GP.
For UK shift workers — common across healthcare, retail and hospitality — irregular hours can make consistent sleep harder to manage. Even with a changing rota, using the calculator to plan sleep around full 90-minute cycles for each specific shift pattern can help reduce grogginess.
Tips for better sleep quality
Frequently asked questions
It's based on the average sleep cycle length (90 minutes) and the average time it takes to fall asleep (about 14 minutes). Individual cycle length can vary slightly, so treat the results as a strong starting guide rather than an exact science.
Six hours covers around 4 complete sleep cycles, which is below the recommended range for most adults. It may feel sufficient occasionally, but regularly sleeping only 6 hours is generally linked to a build-up of sleep debt over time.
That's absolutely fine — the calculator gives you a few options. If you're consistently struggling to fall asleep at any suggested time, it may be worth looking at the sleep debt section above, or reviewing the sleep quality tips.
It depends mainly on age — see the "How Much Sleep Do You Need?" section above for a full breakdown by age group.
This tool is designed around full overnight sleep cycles. For shorter naps, a 20–30 minute nap (avoiding deep sleep stages) or a full 90-minute nap (one complete cycle) tend to work best.
Because 8 hours (480 minutes) doesn't divide evenly into 90-minute sleep cycles, so you're likely to wake up mid-cycle, often during deep or REM sleep. 7.5 hours is exactly 5 complete cycles, ending in light sleep, which is why it can feel more refreshing even though it's less total time.
Four: NREM Stage 1 (light sleep), NREM Stage 2 (core sleep), NREM Stage 3 (deep sleep), and REM sleep. A full cycle through all four stages takes roughly 90 minutes and repeats several times a night.
There's no single best bedtime for everyone — it depends on what time you need to wake up. Use the calculator above in "I want to wake up at" mode to work out bedtime options that align with complete 90-minute sleep cycles for your schedule.