Sleep calculator / Planning guides
Sleep cycles: how to use a cycle calculator
Sleep cycles are repeating sequences of sleep stages, not exact 90-minute appointments. Snoozely uses cycle estimates to offer planning options, but enough total sleep is a better starting point than trying to hit an exact boundary.
What happens during a sleep cycle?
Sleep includes non-REM stages and REM sleep. Your night moves through these stages repeatedly, with the pattern changing as the night progresses. A calculator knows the time you enter and the assumptions you choose; it does not measure your brain activity or determine which stage you will be in when an alarm rings.
How the 90-minute calculation works
At Snoozely’s default settings, five estimated cycles equal 7 hours 30 minutes of sleep. Six equal nine hours and four equal six hours. The calculator adds 15 minutes to fall asleep, separately from the sleep duration. These are arithmetic estimates, not measured cycle lengths. You can change the estimate between 80 and 100 minutes, but a different number still cannot predict your actual stages.
For a 7 AM alarm, five default cycles suggest getting into bed at 11:15 PM. Six suggest 9:45 PM. Four suggest 12:45 AM, but six hours is shorter than the usual adult recommendation. Choosing fewer cycles simply to obtain a convenient bedtime can leave too little rest.
Is eight hours better than five cycles?
Those are different ways of describing a plan. Eight hours is a duration target; five cycles at 90 minutes is 7 hours 30 minutes. There is no need to shorten an eight-hour opportunity to match the second number. Use your required wake-up time, allow time to fall asleep, and adjust your duration based on your needs and daytime functioning.
Choose a useful next step
For a fixed alarm, explore the bedtime guide. For a fixed bedtime, use the wake-up time guide. To understand the difference between time in bed and sleep, read sleep duration.
Open the sleep calculator to adjust your cycle estimate and fall-asleep allowance. If you are tired despite enough sleep opportunity, an exact cycle calculation is unlikely to explain everything. Persistent sleep difficulties deserve professional advice.
Source: NHLBI: sleep phases and stages.
Snoozely is a planning tool for adults. Set a separate alarm. If sleep problems or excessive daytime sleepiness persist, talk to a healthcare professional.