Sleep Calculator
What time should you go to bed — or wake up? This sleep calculator uses 90-minute sleep cycles to find the times that let you wake up between cycles, not in the middle of one, so you rise refreshed instead of groggy. Enter your wake-up time, or tap "sleep now," and get your ideal times in seconds.
Choose what you want to work out, set the time, and we'll show cycle-aligned options. Each option is a full set of 90-minute sleep cycles plus the time it takes to fall asleep.
* These times are based on the well-known model of 90-minute sleep cycles, aiming to have you wake between cycles rather than in the middle of deep sleep. Real cycles vary from about 90 to 110 minutes and differ from person to person and night to night, so treat these as helpful guides, not exact science. Most adults need 7–9 hours of sleep. If you regularly struggle to sleep, wake unrefreshed despite enough hours, or feel persistently tired, consider speaking with a doctor — this tool is for general information only and is not medical advice.
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What Is a Sleep Calculator?
A sleep calculator works out the best time to go to bed or wake up so you rise between sleep cycles instead of in the middle of one. Your sleep runs in repeating cycles of roughly 90 minutes, moving through light sleep, deep sleep, and REM. Wake up mid-cycle — especially during deep sleep — and you feel groggy and foggy. Wake at the end of a cycle and you feel refreshed, even on the same total hours.
This calculator answers the everyday questions: "what time should I go to bed?" if you know when you need to wake, and "what time should I wake up?" if you're heading to bed now. It works anywhere in the world — sleep science is the same everywhere.
How to Use This Sleep Calculator
- Pick your goal — find a bedtime, or find a wake-up time.
- Enter your time — the wake-up time you need, or choose "going to bed now."
- Set how long you take to fall asleep — about 15 minutes for most people.
- Optionally pick your age group — recommended sleep amounts differ by age.
Click Calculate Sleep Times to see your cycle-aligned options, with the best ones highlighted.
How Sleep Cycles Work
A full night isn't one long block of sleep — it's a series of cycles, each about 90 minutes long, repeated five to six times. Each cycle moves through stages:
- Light sleep (N1, N2): the easy-to-wake stages that begin each cycle.
- Deep sleep (N3): physically restorative; waking here causes the worst grogginess.
- REM sleep: dreaming and memory consolidation, growing longer toward morning.
The goal is to time your alarm for the light stage at the end of a cycle, which is why completing whole cycles matters as much as total hours.
The Sleep Calculator Formula
Example: wake at 6:30 AM, 5 cycles (7.5 hrs), 15 min to fall asleep
→ go to bed at 10:45 PM
To find a wake-up time instead, the calculator adds whole 90-minute cycles to the moment you fall asleep. Either way, it lists several options so you can pick the one that fits your schedule — usually aiming for 5 or 6 complete cycles (7.5 to 9 hours).
How Much Sleep Do You Need by Age?
| Age Group | Recommended Sleep | Sleep Cycles |
|---|---|---|
| Children (6–12) | 9–12 hours | 6–8 cycles |
| Teens (13–17) | 8–10 hours | about 6 cycles |
| Adults (18–64) | 7–9 hours | 5–6 cycles |
| Older adults (65+) | 7–8 hours | about 5 cycles |
Why You Wake Up Tired Even After 8 Hours
It's a common puzzle: you sleep a full eight hours and still feel wrecked. The likely reason is that your alarm went off in the middle of a deep-sleep stage rather than at the end of a cycle. Eight hours isn't a whole number of 90-minute cycles (it's about 5.3), so you may be cutting a cycle short. Sleeping 7.5 hours (5 full cycles) or 9 hours (6 cycles) often leaves people feeling better than 8 — because the cycle finished. That's the whole idea behind timing your sleep.
Tips for Better Sleep
- Keep a consistent schedule — same bedtime and wake time, even on weekends.
- Wind down before bed — dim lights and screens in the last hour.
- Watch caffeine — avoid it for several hours before sleeping.
- Keep your room cool, dark, and quiet.
- Get morning daylight — it anchors your body clock.