Sleep Calculator
Enter a wake-up time or bedtime. Get the best times based on sleep cycles.
Best bedtimes
Includes a 14-min fall-asleep buffer. Highlighted = 7.5–9 hrs (recommended for most adults).
How it works
Sleep cycles
Sleep moves through light sleep, deep sleep, and REM in 90-minute cycles. Most adults complete 4–6 per night.
Fall-asleep buffer
Most people take 10–20 minutes to fall asleep. The calculator adds a 14-minute buffer so the times are realistic.
Wake at the right moment
Waking at the end of a cycle — not mid-deep-sleep — is why timing matters. That's what the calculator finds.
How much sleep do I need?
Most adults need 7–9 hours — 5 or 6 complete cycles. Needs vary by age.
| Age group | Recommended sleep | Sleep cycles |
|---|---|---|
| Children (6–12) | 9–12 hours | 6–8 |
| Teenagers (13–18) | 8–10 hours | 5–7 |
| Adults (18–64) | 7–9 hours | 5–6 |
| Older adults (65+) | 7–8 hours | 4–5 |
Consistency matters. A regular bedtime and wake time helps more than any single night of extra sleep. Not medical advice.
Common questions
What time should I go to sleep?
It depends on your wake-up time. For a 7:00 AM alarm, good bedtimes are 9:46 PM (6 cycles, 9 hrs), 11:16 PM (5 cycles, 7.5 hrs), or 12:46 AM (4 cycles, 6 hrs). Enter your wake-up time above for any schedule.
What time should I wake up?
Enter your bedtime above and the calculator shows the best wake-up times. Waking at the end of a 90-minute cycle — not mid-cycle — helps you feel alert instead of groggy.
Why do I feel groggy after 8 hours of sleep?
You probably woke during deep sleep, not at the end of a cycle. Timing your alarm to a cycle boundary — even with slightly less total sleep — often makes a bigger difference than the extra time.
What is a sleep cycle?
One cycle lasts roughly 90 minutes: light sleep, deep sleep, then REM. Most people complete 4–6 per night. Each stage plays a role in physical recovery and memory.
Is this medical advice?
No. It's a planning tool based on general sleep science. If you have ongoing sleep problems, talk to a doctor.