Sleep Calculator
Enter when you need to wake up and find the best bedtime based on 90-minute sleep cycles. Wake up refreshed, not groggy.
Results are based on the widely-used 90-minute sleep cycle model. Individual needs vary — some people feel best with 4 cycles, others need 6. Use this as a starting point.
How the Sleep Calculator Works
Sleep happens in roughly 90-minute cycles. Each cycle moves through light sleep, deep sleep, and REM sleep. Waking up at the end of a cycle leaves you feeling refreshed; waking up mid-cycle is what causes that groggy, hungover feeling — even after 8 hours in bed.
How many cycles do you need?
Most adults need 5-6 cycles per night (7.5 to 9 hours). The calculator shows bedtimes for 3-6 cycles so you can pick what works for your body.
Fall-asleep buffer
The average person takes about 15 minutes to fall asleep. The calculator adds this buffer to each suggested bedtime so you're actually asleep when the cycle begins. Adjust this if you know you fall asleep faster or slower.
Tips for Better Sleep
- Keep a consistent schedule. Go to bed and wake up at the same time every day, even on weekends. Your body's internal clock will adjust within 1-2 weeks.
- Avoid screens 30-60 min before bed. Blue light from phones and TVs suppresses melatonin, the hormone that makes you sleepy.
- Keep your room cool and dark. 65-68°F (18-20°C) is the ideal sleeping temperature for most people.
- Limit caffeine after 2 PM. Caffeine has a half-life of 5-6 hours, so an afternoon coffee can still affect your sleep at midnight.
- Don't hit snooze. Each snooze starts a new sleep cycle you won't finish, making you feel worse. Put your alarm across the room.
Frequently Asked Questions
Most adults need 5-6 complete sleep cycles per night (7.5-9 hours). Each cycle lasts about 90 minutes. Waking at the end of a cycle helps you feel refreshed.
You may be waking mid-cycle. 8 hours = 5.3 cycles. Try 7.5 hours (5 cycles) or 9 hours (6 cycles) instead. Waking at a cycle boundary makes a big difference.
About 15 minutes on average. This calculator adds 15 minutes to each bedtime so you're asleep when the cycle begins. Adjust if you know your own timing.
Best bedtimes: 9:45 PM (6 cycles), 11:15 PM (5 cycles), or 12:45 AM (4 cycles). The 5-cycle option (11:15 PM) is ideal for most adults.