The sleep calculator

Built on 90-minute sleep cycles

The sleep calculator

You don’t wake up groggy because you slept too few hours — often it’s because you woke up mid-cycle. Tell it when you’re getting up or lying down, and it works backward or forward through full 90-minute cycles to find your best windows.

Cycle length varies by 10–15 minutes from person to person, and the fall-asleep buffer used here (15 minutes) is an average, not yours specifically — treat these as strong starting windows, not a guarantee. Ongoing trouble falling or staying asleep is worth raising with a doctor rather than solving with timing alone.