Teens aren’t getting enough Sleep, concludes an analysis by Jean Twenge, a San Diego State psychology professor.

In two surveys, 40 percent of adolescents reported sleeping less than seven hours a night in 2015. That’s way up from past estimates.

“The more time young people reported spending online, the less sleep they got,” the report noted. “Teens who spent five hours a day online were 50 percent more likely to not sleep enough than their peers who only spent an hour online each day.”

Teens who sleep for less than eight hours are sleep-deprived, writes researcher Kyla Wahlstrom. “Yet, the average teen in America obtains less than seven hours of sleep on a School night.”

Nearly half of U.S. high schools start before 8 am, and more than 85 percent start before 8:30, she writes. When schools push back start times, “students do in fact get more sleep, tending to go to bed at the same time but getting to rise a bit later in the morning,” Wahlstrom’s research has found. “Their academic performance improves significantly.”

Starting school later — say at 8:30 am — would improve students’ academic performance, driving, health and the U.S. economy, according to a RAND analysis.

Over 15 years, the U.S. economy would benefit by $9.3 billion annually, the study estimates. That doesn’t include possible benefits in reducing suicides, obesity and mental-health problems, all of which are linked to insufficient sleep.