Calculate the best times to wake up or go to sleep based on 90-minute sleep cycles.
Waking up mid-sleep cycle — when you're in deep sleep — is responsible for that heavy, groggy feeling that can ruin the first half of your morning even if you got enough hours. Sleep cycles run roughly 90 minutes each, and timing your alarm to the end of a cycle rather than the middle makes a real difference.
This calculator works in two directions: enter your bedtime and it tells you the best times to set your alarm, or enter when you need to wake up and it tells you when to go to bed. Either way, it's targeting the lighter sleep stages at the end of each 90-minute cycle, which is when waking feels most natural.
It also adds 15 minutes to account for the time it takes most people to fall asleep after lying down. If you tend to fall asleep faster or slower than that, you can adjust accordingly.
Most adults need 5-6 complete cycles per night, which equals 7.5-9 hours of sleep. Some people function well on 4-5 cycles but this is less common. Consistently getting fewer than 4 cycles (6 hours) is associated with a range of health issues over time.
It's an average. Individual cycles range from about 80-110 minutes. If you consistently feel best waking at a time slightly outside what this calculator suggests, your cycles may just be slightly shorter or longer than average.
Going to bed at the same time every night — even on weekends — is one of the most effective ways to regulate your sleep-wake cycle. Reducing screen exposure in the hour before bed and keeping your bedroom cool and dark also make it significantly easier to fall asleep on schedule.
Yes — a 10-20 minute nap in the early afternoon can restore alertness without significantly disrupting nighttime sleep. A 30-60 minute nap risks entering deep sleep and causing grogginess. A full 90-minute nap completes one cycle and can be genuinely restorative.