Understanding 90-Minute Sleep Cycles
Sleep is not a continuous state; it occurs in cycles. The average human sleep cycle lasts about 90 minutes. During this time, your brain moves through different stages including Light Sleep, Deep Sleep, and REM.
Waking up in the middle of a deep sleep cycle often results in "sleep inertia" (that groggy, zombie-like feeling). To feel rested, it is best to wake up at the end of a cycle, when your sleep is naturally lighter.
How this Calculator Works
- Wake Up Mode: If you want to wake up at 7:00 AM, we calculate backwards. We assume you are ending Cycle 1 at 7:00 AM. To achieve this, you must be in bed by approximately 5:30 AM (allowing 14 minutes to fall asleep).
- Bedtime Mode: If you want to go to bed at 10:30 PM, we calculate forward. We assume you are starting Cycle 1 at 10:30 PM. You will likely wake up naturally at the end of Cycle 1 (approx. 12:00 AM) or you can set an alarm for the end of a later cycle.
Recommendations
- Adults (18-64): Typically need 7–9 hours (5-6 cycles). 5 cycles is often the sweet spot.
- Teenagers: Need 8–10 hours of sleep.
- Consistency: Going to bed and waking up at the same time every night reinforces your body's circadian rhythm.