Most adults need about 1.5 to 2 hours of deep sleep per night, which typically accounts for around 20-25% of total sleep time. For example, if you sleep 7 to 8 hours, spending roughly 1.5 to 2 hours in deep sleep is considered healthy and crucial for physical repair, immune system strengthening, and overall well-being. This amount may vary with age, health, and physical activity level, but maintaining this range helps ensure restorative sleep and feeling well-rested during the day.