Those calculations should be taken with a grain of salt: Sleep cycle length of 90 minutes is just a rough average. It varies throughout the night and gets affec

Those calculations should be taken with a grain of salt: Sleep cycle length of 90 minutes is just a rough average. It varies throughout the night and gets affected by other factors, like sleep deprivation. There are also individual differences. Even more important than the amount of sleep is a consistent go-to-bed time. People tend to sleep better if they do it around the same time every night, maintaining a consistent biological day-night cycle.