WASHINGTON – College, as the saying goes, is supposed to be the best four years of your life. But there’s increasingly a new norm for students: spending six years getting a degree.

Even the government now measures whether students graduate on time if they do it within six years, rather than four.

Taking longer to graduate isn’t cheap. It costs $15,933 more in tuition, fees and room and board for every extra year at a public two-year college and $22,826 for every added year at a public four-year college, according to a new report by the nonprofit Complete College America.

At a time when total student debt has surpassed $1 trillion, getting students to graduate on time has become critical.

So what’s the reason behind students spending so much extra time getting their degrees?

Colleges have added too many unnecessary degree requirements and remedial courses that keep students in school for much longer than needed, according to the report.

A recent Education Department study found that the average graduate had accumulated 138.4 credits by the time he or she received a bachelor’s degree, when 120 is usually sufficient. Tack on another 20.3 credits for the average amount of courses that students fail, repeat or withdraw from, and those credit hours jump to 158.7 credits earned or attempted. At an estimated cost of $361 per credit, those credits start to add up.

“Most colleges and universities raise tuition and fees each year, while financial aid stays nearly constant,” researchers wrote. “As scholarships and savings run out, students and their families are left to borrow more of the costs of attending school.”

Administrators at Temple University and University of Texas at Austin, for example, told researchers that two extra years at their campuses increase debt by nearly 70 percent among students who borrow.

If schools want to rein in costs for students, Complete College America recommends they streamline curricula and cap the number of credit hours needed for bachelor’s degree at 120 hours and for an associate degree at 60 hours.

Those hours already are the standard for a majority of degrees, though some schools have let departments pile on additional course work over the years. Capping credit hours, the report says, would make it easier for students to graduate on time as long as they take 15 credit hours a semester.

Carrying a full course load, however, may not work for students juggling school, work and family, not to mention those who simply can’t afford the cost.

Nearly two thirds of students at community colleges, for instance, attend part-time because of those sorts of obligations, according to data from the American Association of Community Colleges. Earning an associate’s in two years would certainly reduce costs for those students, but increasing their grant aid would arguably be more effective.

Still, schools could do a better job of creating a more direct route to graduation, the report says. Offering more sections of core classes, accepting transfer credits or simply monitoring students’ course loads are just some of the strategies colleges could use to increase on-time graduation.

As it stands, only 50 out of the more than 580 public four-year institutions report on-time graduation rates at or above 50 percent for their first-time, full-time students, according to the Education Department’s Integrated Postsecondary Education Data System, or Ipeds.

At the University of Arizona, only 34 percent of students graduate within six years, according to Department of Education data. At Michigan State University, it’s 48 percent. Overall, at flagship universities, only 36 percent of students are getting their degrees after six years.

Another part of the problem, according to Complete College America, is the “broken” system of remedial courses that students with weak academic records are required to take.

About 20 percent of college students are enrolled in remedial classes, according to the most recent data from the Education Department. That means they must take courses in math or English to help them catch up to the rest of their classmates. But those classes don’t count toward a degree and tend to delay students from graduating on time.

Complete College America wants schools to offer remediation alongside college-level courses, instead of having students take remedial classes before their core courses. Think of it as intensive tutoring.