Sleep Calculator

Waking groggy despite enough hours is caused by waking mid-cycle. Sleep happens in 90-minute cycles. Waking at cycle end leaves you alert and refreshed. Mode 1: Enter your wake-up time. The tool shows ideal bedtimes for 4 to 8 complete 90-minute cycles. Mode 2: Click Use current time. See ideal wake-up times at the end of each cycle. The calculator adds 14 minutes for average sleep latency after lying down. Sleep stages: Stage 1 and 2 are light sleep. Stage 3 is deep slow-wave sleep, the most restorative. Stage 4 is REM sleep where dreaming and memory consolidation occur. Each full cycle is 90 minutes. Adults need 5 to 6 cycles per night (7.5 to 9 hours). Consistently fewer than 5 cycles builds sleep debt that impairs focus, mood, and health. Nap guide: A 20-minute nap stays in light sleep. A 90-minute nap completes one full cycle. Naps of 30 to 60 minutes end during deep sleep, causing grogginess on waking. Sleep hygiene: Keep a consistent wake time every day. Avoid screens 30 minutes before bed. Keep your room cool and dark. Avoid caffeine after 2pm.