Free Chrome extension · by Hypnothera
Sleep cycle calculator
Sleep Window is a free Manifest V3 Chrome extension. Enter a wake time or bedtime and get 90-minute cycle windows (3–6 cycles) so you can plan a night around a simple schedule heuristic — not a medical claim.
Popup-only · local storage · no account · view source on GitHub
A bedtime / wake planning heuristic
Popular sleep-timing guides often talk about ~90-minute cycles. Sleep Window turns that idea into a small Chrome popup: choose when you want to wake or when you plan to go to bed, and see windows for 3, 4, 5, or 6 cycles. Use it as a schedule aid alongside whatever bedtime routine already works for you.
Hypnothera is a personalized hypnosis app that creates original guided audio around each user's goals, words, preferred voice, and session length. Sleep Window is the free Chrome companion for people who want a quick cycle calculator next to that.
What's in the extension
Wake or bedtime → windows
Pick when you need to wake, or when you plan to sleep. Sleep Window maps 3–6 ninety-minute cycle windows around that time.
5-cycle / 7.5h highlighted
A common planning default — five cycles (~7.5 hours) — is called out so you can aim for a familiar middle ground.
Fall-asleep buffer + wind-down
Add a 0–30 minute fall-asleep buffer (default 14). Optional local reminder and a 2-minute wind-down breathing exercise in the popup.
Zero data collection
Manifest V3, popup-only. Preferences stay in local chrome.storage. Nothing is sent to a server.
Cycle durations at a glance
Approximate totals from whole 90-minute blocks (before your fall-asleep buffer). Five cycles / ~7.5 hours is highlighted in the extension as a common planning default.
| Cycles | Approx. duration |
|---|---|
| 3 | 4.5 hours |
| 4 | 6 hours |
| 5highlighted default | 7.5 hours |
| 6 | 9 hours |
Questions, answered
Is this a medical sleep tool?
No. Sleep Window is a planning heuristic for bedtime and wake windows based on commonly discussed ~90-minute sleep cycles. It is not a medical device, diagnosis, or treatment, and it does not claim to improve sleep outcomes.
Why 90-minute cycles?
Many popular sleep-timing guides use ~90-minute blocks as a simple schedule rule of thumb. Real sleep architecture varies by person and night. Treat the windows as planning aids, not prescriptions.
Does Sleep Window collect my data?
No. The extension does not collect analytics or personal data. Settings and reminders use local chrome.storage only, on your device.
Does it work offline?
Yes. After you install it from the Chrome Web Store, the popup calculator runs locally in Chrome. You do not need an account or an internet connection to use it.
Who makes Sleep Window?
Hypnothera — a personalized hypnosis app that creates original guided audio around each user's goals, words, preferred voice, and session length. Sleep Window is a free companion Chrome extension.
Plan tonight's windows in Chrome
Install Sleep Window free from the Chrome Web Store — or make a bedtime hypnosis script when you want guided audio from Hypnothera.