Most healthy adults need about 1 to 2 hours of deep sleep per night, but there is no exact number that applies to everyone. Deep sleep usually makes up about 13% to 25% of total sleep, so getting enough overall sleep is the most important starting point.
Deep sleep is the stage of sleep linked with physical recovery, immune function, and some parts of learning and memory. It tends to happen more in the first half of the night and usually decreases with age, so older adults may naturally get less deep sleep than younger adults.
A sleep tracker may estimate deep sleep, but these numbers are not always exact. It is more useful to look at how you feel during the day, whether you wake often at night, and whether you are getting enough total sleep on a regular schedule.
If you often feel very tired despite spending enough time in bed, wake up gasping, snore heavily, or have restless sleep, it is best to speak with a sleep specialist. Treating problems that interrupt sleep can help improve deep sleep naturally.