Why sleep cycles matter – Sleep is a critical pillar of health; high-quality sleep supports your immune system, cardiovascular function and cognitive performance. Each cycle (about 90 minutes) includes light sleep, deep sleep and REM sleep. Waking up in the middle of a cycle can leave you feeling groggy and compromise your mood and focus. In contrast, waking at the end of a complete cycle helps you feel more refreshed and alert. Getting enough sleep each night allows your mind and body to reap these restorative benefits. Use the calculator to plan bedtimes or wake-up times that align with full cycles—and tap the “Copy” button to quickly set your alarm for the best results.