How This Works

Sleep isn't one continuous state — it moves through repeating cycles of roughly 90 minutes, each containing light sleep, deep sleep, and REM. Waking up in the middle of a cycle (especially during deep sleep) is what makes mornings feel groggy, even after 8 hours in bed.

Shush calculates your ideal bedtime or wake-up time by counting backward or forward in full 90-minute cycles, so you wake up between cycles instead of in the middle of one. Most adults feel most rested after 5–6 complete cycles (7.5–9 hours).

Weather, light exposure, and evening habits also affect how easily you fall asleep and how deep your sleep is — that's why we factor in local weather above when available.