Sleep Calculator
Find the best time to go to bed — or wake up — based on 90-minute sleep cycles, so your alarm goes off between cycles instead of mid–deep sleep.
I need to wake up at…
…or I'm going to bed at…
How sleep cycles work
During the night you move through repeating cycles of light sleep, deep sleep and REM (dreaming) sleep. Each cycle lasts roughly 90 minutes. Deep sleep dominates the early cycles; REM gets longer towards morning.
Being woken during deep sleep is what causes sleep inertia — that heavy, confused feeling that can last 15–30 minutes. Timing your alarm to land at the end of a cycle, when sleep is lighter, makes waking up easier.
Tips for a better wake-up
- Keep the same wake-up time every day, including weekends.
- Get daylight in the first hour after waking.
- Avoid caffeine in the 6–8 hours before bed.
- Pick a gentle alarm sound — see our guide to the best alarm tones.
Bedtimes for common wake-up times
Each page shows the ideal bedtimes and lets you set the alarm in one click:
4:00 AM4:15 AM4:30 AM4:45 AM5:00 AM5:15 AM5:30 AM5:45 AM6:00 AM6:15 AM6:30 AM6:45 AM7:00 AM7:15 AM7:30 AM7:45 AM8:00 AM8:15 AM8:30 AM8:45 AM9:00 AM9:15 AM9:30 AM9:45 AM
This calculator is for general information only and is not medical advice.
Sleep calculator FAQ
How does the sleep calculator work?
It counts backwards (or forwards) in 90-minute sleep cycles and adds about 15 minutes to fall asleep. Waking at the end of a cycle, during light sleep, tends to feel less groggy than waking from deep sleep.
How many sleep cycles do I need?
Five to six cycles (7.5–9 hours) suits most adults. The US CDC recommends at least 7 hours per night for adults aged 18–60.
Are sleep cycles always 90 minutes?
No — cycles typically range from about 80 to 120 minutes and vary between people and across the night. 90 minutes is a practical average, so treat the results as a starting point and adjust by 10–15 minutes if you still wake up tired.
How long does it take to fall asleep?
Healthy adults usually fall asleep in 10–20 minutes. If you consistently take much longer, or fall asleep instantly, it may be worth talking to a doctor.