Sleep Cycle Calculator

[Please note first] This app has no alarm and no notifications. It cannot wake you at a set time. It does not keep a diary of the hours you have slept. It gives no advice about sleep quality or your body, and no recommended hours by age. All it produces are times worked out by adding and subtracting. ────────── ◔ Sleep Cycle Calculator — four times that land on a cycle Deep sleep and light sleep come round together as one cycle, over and over. Waking at the join between two cycles is said to feel easier than waking in the middle of one, even for the same number of hours. A cycle of about 90 minutes is the figure in common use. ■ Two directions Going to bed now — enter the time you are turning in, get four wake-up times Want to wake at — enter the time you must be up, get four bedtimes Tap the tab at the top to switch between them. ■ An answer is already on screen The bedtime side starts from the time you opened the app, so you can open it in bed and simply read the four times. Nothing needs typing first. ■ 15 minutes to fall asleep is included You do not fall asleep the moment you get into bed, so 15 minutes is allowed for before the cycles start. Leave it out and every time shifts by 15 minutes. Going to bed at 23:00 4 hr 30 min — 03:45 6 hr — 05:15 7 hr 30 min — 06:45 9 hr — 08:15 Wanting to wake at 07:00 4 hr 30 min — 02:15 6 hr — 00:45 7 hr 30 min — 23:15 (day before) 9 hr — 21:45 (day before) Times that fall on another date are marked "next day" or "day before", so there is nothing to misread. ■ Not exactly 90 minutes A cycle runs anywhere from 70 to 120 minutes, and it varies from person to person and from night to night. What comes out of this sum is a set of suggestions, not one right answer. That is why four of them are offered. ■ The four lengths 4 hr 30 min, 6 hr, 7 hr 30 min, 9 hr — three, four, five and six cycles. The same four appear whichever direction you are working in. ■ Subtracting is the awkward part To get from "up at seven" to a bedtime you take an hour and a half away three to six times over, and 15 minutes on top of that. The borrowing is what makes it easy to get wrong in your head, and it is what this app is for. ■ How to enter a time Type an hour and a minute: hours from 0 to 23, minutes from 0 to 59. Common times are on buttons (bed at 22:30, 23:00, 0:00 and 1:00; waking at 6:00, 6:30, 7:00 and 7:30). ■ Things worth knowing (included in the app) ▪ Deep sleep and light sleep come round together as one cycle ▪ Waking at the join between two cycles is said to feel easier ▪ A cycle is about 90 minutes, but anywhere from 70 to 120 minutes ▪ 15 minutes is allowed for falling asleep; leave it out and everything shifts ▪ What you get are suggestions, not answers ■ How the app is built ▪ A single screen. No settings page ▪ Your last five entries are kept and can be tapped to restore ▪ The four times copy with one tap ▪ Japanese and English, following your device language ▪ No account needed. Every sum runs on your device and the times you type are never sent anywhere ────────── Note: this app has no alarm and no notifications, and cannot wake you at a set time. It keeps no diary of your sleep. It offers no advice about sleep quality or your body, no recommended hours by age, and no nap times. It does not convert between time zones.