Sleep Window Calculator
Plan your bedtime inside the hours you are actually free to sleep — built from full 90-minute cycles.
Sleep Window Helper
Choose the time range you are free to sleep. We find the best bedtimes that complete full 90-minute cycles and wake you inside your window.
How the sleep window calculator works
A sleep window calculator starts from the hours you are free to sleep — say 10 PM to 7 AM — rather than a fixed bedtime. It works forward in 15-minute steps, keeping only the bedtimes whose full 90-minute cycles end inside your window. The result is a list of bedtimes that fit your real schedule and still complete whole cycles.
If your evenings are unpredictable, this is more useful than a single bedtime. You see every option that lands you on a cycle boundary and wakes you inside your window — so you can pick the one that suits the night.
Why plan around a window?
Real life is not a fixed clock. A window respects your constraints (work, childcare, shift patterns) while still protecting sleep quality by completing full cycles. The 90-minute model here follows sleep science such as the National Sleep Foundation's duration guidance (2022). Most adults do best with 4–6 cycles; the helper tells you how many your window can hold.
A few quick tips
- Make the window at least 6–9 hours for an adult.
- Earlier bedtimes inside the window give more margin.
- Compare with the Bedtime and Wake-up tools for a single target.
Frequently asked questions about the Sleep Window Helper
Everything you need to plan around your free hours.
Explore more sleep tools
Each one plans sleep around your 90-minute cycles.