Find the best wakeup and bedtimes based on natural 90-minute sleep cycles. Optimize your rest, prevent morning grogginess, and sleep better to boost health.
Each sleep cycle is 90 min. Allow ~15 min to fall asleep.
Waking up feeling tired often has less to do with the total hours you slept and more to do with waking up in the middle of a deep sleep cycle. Our free online Sleep Calculator helps you determine the best times to fall asleep or wake up, calculating times in 90-minute intervals to ensure you wake up at the end of a natural sleep cycle.
A normal sleep cycle consists of five stages and lasts approximately 90 minutes. Waking up at the end of a cycle, rather than during deep sleep (stages 3 or 4), prevents sleep inertia (grogginess). The calculator factors in the average 15 minutes it takes to fall asleep to give you precise bedtime and wakeup recommendations.
A natural sleep cycle lasts approximately 90 minutes. A typical night of healthy sleep consists of 5 to 6 complete sleep cycles, translating to 7.5 to 9 hours of sleep.
If you wake up in the middle of a deep sleep cycle, you will experience sleep inertia, making you feel groggy and tired. The sleep calculator helps you time your wakeup to coincide with the end of a 90-minute cycle instead.
Most adults need between 7 and 9 hours of sleep per night to function optimally, which corresponds to 5 or 6 complete sleep cycles.
The calculator takes your desired wakeup time, subtracts sleep cycles in 90-minute increments (e.g., 7.5 or 9 hours), and subtracts 15 minutes for the average time it takes to fall asleep, telling you the exact time to go to bed.