How to use
- Choose whether you know your wake-up time or your bedtime.
- Enter the time and how long you usually take to fall asleep (15 minutes is typical).
- Pick one of the suggested times; 5 or 6 cycles (7.5 to 9 hours) are marked as best.
Worked example: Waking at 6:30 AM
Counting back six 90-minute cycles plus 15 minutes to fall asleep gives a bedtime of 9:15 PM for 9 hours of sleep. Five cycles gives 10:45 PM for 7.5 hours, four gives 12:15 AM and three gives 1:45 AM.
If you go to bed at 11:00 PM instead, the wake times are 4:15 AM, 5:45 AM, 7:15 AM and 8:45 AM.
Frequently asked questions
Why 90 minutes?
A full sleep cycle through light, deep and REM sleep averages about 90 minutes. Waking at the end of a cycle usually feels easier than waking in deep sleep.
How many cycles should I aim for?
Most adults do best with five or six cycles, 7.5 to 9 hours. The calculator marks those as best.
What is the fall-asleep time for?
Sleep cycles start when you actually fall asleep, so the minutes you spend drifting off are added before the first cycle.
What does "If I go to bed now" do?
It fills in the current time as your bedtime and lists wake-up times from now.
Is this medical advice?
No. It is a simple model; individual cycles vary from about 70 to 120 minutes.
Can I change the cycle length?
Not in this version. The 90-minute average is used.