Best bedtimes or wake times based on sleep cycles.
Free to use, no sign-up required. Sleep Calculator is one of 198 tools built into Xenition, alongside a chat that can use them for you.
Times sleep in whole 90-minute cycles, so you wake at the end of a cycle rather than in the middle of one. Choose the time you know, bedtime or wake time, and it gives you the other. It is a guide, not medical advice.
One cycle is counted as 90 minutes and falling asleep as 15 minutes. From a wake time, each option is wake time − (cycles × 90 + 15) minutes, which is when to be in bed. From a bedtime, it is bedtime + (cycles × 90 + 15). Six cycles is 9 hours of sleep, five is 7.5 and four is 6.
To wake at 07:00, go to bed at 9:45 PM for 6 cycles, 11:15 PM for 5 or 12:45 AM for 4. Going to bed at 23:00 gives wake times of 8:15 AM, 6:45 AM and 5:15 AM.
On average. Individual cycles run roughly 80 to 110 minutes and change through the night, so treat the times as a starting point and adjust by 10 to 15 minutes.
Most health bodies recommend 7 to 9 hours for adults, which is why 5 cycles (7.5 hours) and 6 cycles (9 hours) are highlighted.
You do not have to open Sleep Calculator to use it. Ask Xenition in plain language and it runs the right tool, then carries the answer into whatever you are working on — a document, a spreadsheet, a deck.