The vast majority of students at American public colleges do not graduate on time, according to a new report from Complete College America, a nonprofit group based in Indianapolis.

“Students and parents know that time is money,” said the report, called “Four-Year Myth.” “The reality is that our system of higher education costs too much, takes too long and graduates too few.”

At most public universities, only 19 percent of full-time students earn a bachelor’s degree in four years, the report found. Even at state flagship universities — selective, research-intensive institutions — only 36 percent of full-time students complete their bachelor’s degree on time.

Nationwide, only 50 of more than 580 public four-year institutions graduate a majority of their full-time students on time. Some of the causes of slow student progress, the report said, are inability to register for required courses, credits lost in transfer and remediation sequences that do not work. The report also said some students take too few credits per semester to finish on time. The problem is even worse at community colleges, where 5 percent of full-time students earned an associate degree within two years, and 15.9 percent earned a one- to two-year certificate on time.