Sleep Calculator
FAST · FREE · PRIVATE
Wake up between sleep cycles instead of in the middle of one.
Pick wake-up or bedtime, set it, then tap Calculate.
General guidance only, not medical advice.
Last updated · By Infinity Tools
Frequently Asked Questions
How the sleep calculator works
The Infinity Sleep Calculator counts in whole sleep cycles of about 90 minutes and adds 15 minutes to fall asleep, so your alarm goes off near the end of a cycle, when sleep is lightest. Six cycles (9 hours) is marked Best, five cycles (7 h 30 min) Good and four cycles (6 hours) OK.
Example: to wake up at 6:30 AM, go to bed at 9:15 PM (six cycles), 10:45 PM (five cycles) or 12:15 AM (four cycles).
How long is a sleep cycle?
About 90 minutes. During a typical night, sleep moves through cycles of light sleep, deep sleep and REM sleep about every 90 minutes, and each cycle begins and ends with lighter sleep (National Sleep Foundation).
Why does the calculator add 15 minutes?
The calculator allows 15 minutes to fall asleep, the classic sleep-calculator assumption, and starts counting sleep cycles after that. The National Sleep Foundation counts falling asleep within 30 minutes as a sign of good sleep quality (National Sleep Foundation). If you usually take longer than 15 minutes, go to bed a little earlier.
How many hours of sleep do adults need?
Seven to nine hours a night for adults aged 18 to 64, and seven to eight hours after 65 (National Sleep Foundation). Yet 35% of adults in the U.S. report sleeping less than seven hours a night (National Sleep Foundation). Five cycles (7 h 30 min) and six cycles (9 hours) fall within the recommended range. Four cycles (6 hours) is a short night.
Why do I wake up groggy even after enough sleep?
Waking in the middle of deep sleep causes sleep inertia, the heavy, foggy feeling that can hang around after the alarm. Because sleep cycles begin and end with lighter sleep, you may feel more refreshed if you wake up at the end of a cycle (National Sleep Foundation). Read more in Why you wake up groggy, and how to stop it.
Does it work for naps or shift work?
Yes. Nap mode times a 20-minute power nap or a 90-minute full cycle, and Shift workers mode plans sleep around a shift that ends in the morning or starts early.