Wake up refreshed. Find the perfect bedtime or wake-up time based on your natural 90-minute sleep cycles.
Sleep happens in cycles of roughly 90 minutes. Each cycle moves through light sleep, deep sleep, and REM. Waking up at the end of a cycle — rather than in the middle of deep sleep — is what makes you feel rested. This calculator adds 15 minutes to your sleep time to account for falling asleep, then maps out complete 90-minute cycles.
Most adults need 5 to 6 complete sleep cycles per night, which equals 7.5 to 9 hours of sleep. Waking after 4 cycles (6 hours) is manageable short-term, but consistently getting 5–6 cycles is essential for memory, focus, and immune health.
You likely woke up mid-cycle. Sleeping "too long" often means your alarm interrupted deep sleep, triggering sleep inertia — that heavy, groggy feeling. Waking at the end of a 90-minute cycle, even with fewer total hours, typically feels much better.
For most adults, the sweet spot is between 10 PM and midnight. Your body's circadian rhythm produces the most melatonin between 9–11 PM. Sleeping during this window aligns with your natural biology and tends to produce deeper, more restorative sleep.
Yes — a 20-minute nap (before 3 PM) can restore alertness without disrupting your nighttime sleep. A full 90-minute nap completes one cycle and can partially compensate for lost deep sleep. Avoid napping longer than 90 minutes as it risks creating sleep inertia.
Both matter, but quality often drives more of how you feel. Consistent schedule, a dark room, and avoiding screens 30–60 minutes before bed dramatically improve cycle quality — meaning you get more deep sleep and REM within the same hours.