If you’re unsure what your ideal sleep number is, play around with setting an alarm so you get 7.5 hours and nine hours of sleep to start, corresponding to five and six sleep cycles, respectively. Note how you feel upon waking, and track your findings in a sleep diary. Add details about what time you got in bed, what time you woke up, what you did in the hours leading up to bed, and what (and when) you ate the night before to get a more complete picture of the habits that enhance or harm your sleep.

Once you find your ideal number—or ideal range—stick to it! When it comes to sleep, the experts stress that consistency is key. That means going to bed and waking up at around the same time every day, even on weekends. Pelayo adds that it’s important to leave yourself some wiggle room, too. So if you know you need 7.5 hours of sleep to function at your best, don’t get into bed exactly 7.5 hours before your alarm is set to go off.

“As you get older and life gets more complicated, you learn the amount of sleep you need, and that’s what you home in on,” he says, adding that constantly teetering on a razor’s edge like this can make you more vulnerable to the unfortunate side effects of a night of poor sleep. “If you always sleep as little as possible and then don’t sleep, the next day you’re a basket case.”

https://www.mindbodygreen.com/articles/not-everyone-needs-8-hours-of-sleep-how-to-find-your-ideal-amount