Sleep Calculator
Find the best times to go to bed or wake up so you finish a full 90-minute sleep cycle and wake feeling rested.
Sleep cycles
Sleep runs in cycles of roughly 90 minutes. Each cycle moves through light sleep, deep sleep and REM (dreaming) sleep. Waking at the end of a cycle, when sleep is light, usually feels easier than waking from deep sleep in the middle of one, which can leave you groggy (sleep inertia).
The calculator counts back (or forward) in 90-minute steps from the time you choose, and adds the time it typically takes you to fall asleep.
To wake at 7:00 AM after five or six full cycles, with 15 minutes to fall asleep, aim to be in bed around 9:45 PM or 11:15 PM.
How much sleep do adults need?
| Age | Recommended sleep |
|---|---|
| Teenagers (14–17) | 8–10 hours |
| Adults (18–64) | 7–9 hours |
| Older adults (65+) | 7–8 hours |
Source: US National Sleep Foundation. Five cycles (7.5 hours) or six cycles (9 hours) fit these ranges well.
Tips for better sleep
- Keep the same wake-up time every day, including weekends.
- Get daylight in the morning and dim screens in the hour before bed.
- Avoid caffeine after early afternoon; its effects last 6 hours or more.
- Keep the bedroom cool, around 18 °C (65 °F), dark and quiet.
Cycle length varies between people and across the night, so treat the times as a guide and adjust by 15–30 minutes to suit you.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, though individual cycles range from roughly 70 to 120 minutes.
Is it better to sleep 6 or 7.5 hours?
For most adults, 7.5 hours is better. It provides five complete cycles and falls within the recommended 7–9 hours.
Why do I feel tired after 8 hours of sleep?
You may be waking mid-cycle, sleeping poorly, or have an underlying issue such as sleep apnea. If tiredness persists, talk to a doctor.
Last reviewed Oct 20, 2026. Results are estimates; check important decisions with a qualified professional.