The number of hours of deep sleep needed depends on the person and the situation. Generally, the longer one has been awake, the more hours of deep sleep their body will need to repair fully and for the individual to feel fully rested.
However, the exact number of hours still varies significantly from person to person because of complex factors like age and genetics. The older a person gets, the less deep sleep they need. Younger children need more deep sleep because it is a crucial period for physical growth and development.
On average, it is recommended that adults 18 years and older try to get about 1.5-2 hours of deep sleep every night. Because deep sleep is usually around 20% of sleeping time, this requires about 8 hours of sleep per night.
Chronic sleep deprivation has been associated with shorter life expectancy, a host of health problems, and significantly lowered levels of cognitive function. It’s simply not possible to function at your best if you’re not getting the sleep you need. Additionally, there are serious, long-term health consequences so complex they are still not fully understood.