Sleep Calculator —
Wake Up Refreshed

Our sleep calculator uses 90-minute sleep cycles — the natural rhythm your brain follows each night. It adds 14 minutes (average fall-asleep time) to your bedtime, then calculates wake-up times at the end of 1–6 complete cycles. Waking at the end of a cycle means you surface from light sleep, feeling refreshed rather than groggy.

Adults (18–64) need 7–9 hours per night; 7.5 hours (5 sleep cycles) is optimal. Teenagers need 8–10 hours, school-age children 9–12 hours, and older adults (65+) need 7–8 hours. These CDC and NHS recommendations vary by age — use our Sleep by Age Calculator for your specific number.

Sleep inertia occurs when your alarm pulls you out of deep sleep (N3 stage) rather than at the end of a natural cycle. Even 8 hours can be poorly timed. Our calculator prevents this by recommending times aligned with the end of complete cycles, so you rise during light sleep.

It depends on your wake-up time. For a 6:30 AM alarm: optimal bedtime is 10:47 PM (5 cycles). Good: 12:17 AM (4 cycles). Minimum: 1:47 AM (3 cycles). Use our Bedtime Calculator for any wake time.

Six hours (4 cycles) is adequate short-term, but chronically insufficient for most adults. The CDC and NHS recommend 7–9 hours. Studies show regular sub-7-hour sleep causes cognitive impairment, weakened immunity, and increased risk of chronic disease over time.

Partially. Recovery sleep can restore some alertness, but the cumulative health impacts of chronic sleep debt do not fully reverse. Consistent 7–9 hour nights are the only sustainable solution. Use our Sleep Debt Calculator to estimate your deficit.

REM (Rapid Eye Movement) sleep is the final stage of each sleep cycle, making up ~25% of total sleep. It is when you dream, consolidate memories, process emotions, and restore creativity. REM increases with each successive cycle — skipping your last cycle disproportionately reduces your total REM sleep.