Sleep Calculator

Calculate optimal bedtime or wake-up time based on 90-minute REM sleep cycles.

Sleep happens in roughly 90-minute REM cycles. Waking at the end of a cycle leaves you refreshed; waking mid-cycle leaves you groggy. This tool gives you the times to either go to sleep (if you know when you must wake) or wake up (if you know when you went to sleep), aiming for full cycles.