How much is too much to pay for college? | Opinion

About three-fourths of students who attend four-year colleges graduate with loan debt. That's up from about half of students three decades ago.

Whether students have debt — and how much — depends greatly on the school they attend. Graduates of private colleges, for instance, are more likely than those from public institutions to have debt. Students who attend wealthy selective colleges — some of which cover the full cost of attendance for financially needy students — are less likely to have debt than those who attend expensive lower-tier colleges.

Unlike a mortgage or a car loan, student loans aren't based on complicated formulas about what an applicant can afford to pay. The federal government suggests that no more than 15 percent of income should go toward paying student-loan debt. But the problem is few high school seniors know what they might earn in the decade after college when they will be paying off their loans.

At this time of year, as high school seniors and parents weigh college decisions and financial aid offers, the question I inevitably get is this: How much is too much debt to take on to pay for an undergraduate degree?

Recently, I asked a few experts to weigh in on this question. Several told me a rule of thumb is that total undergraduate borrowing should be limited to what you might expect to make your first year after graduation. By that measure, many college graduates seem to be doing well: Average debt is about $37,000 and first-year salaries are close to $40,000, on average.

"If total debt is less than annual income, you should be able to repay your student loans in 10 years or less," said Mark Kantrowitz, an author of four books on financial aid.

But others said an appropriate amount of debt shouldn't be defined by one data point because there are too many variables — from family finances to choice of school and major.

"Debt in an amount that causes the students or the family stress — whether before, during or after college — is too much debt," said Sara Goldrick-Rab, author of "Paying the Price: College Costs, Financial Aid, and the Betrayal of the American Dream" and a professor at Temple University.

Andrew B. Palumbo, dean of admissions and financial aid at Worcester Polytechnic Institute, said how much to borrow for college "is an inherently personal decision that is best made after conducting thoughtful research."

Students and their parents, he said, "should know their school's graduation rate, loan default rate and the likely return on investment for the major they choose."

Such information is easily found because of a bevy of consumer-friendly Web sites introduced in recent years. Most useful is the College Scorecard from the U.S. Department of Education (collegescorecard.ed.gov), which includes five key pieces of data about a college: costs, graduation rate, loan default rate, average amount borrowed and employment.

The College Scorecard is not without shortcomings. When it comes to earnings after graduation, a student's major matters, so institutional data is not as helpful as information specific to individual academic programs.

In seven states — Colorado, Florida, Minnesota, Tennessee, Texas, Virginia and Washington — students can search public databases for yearly earnings of graduates of institutions within the state, by major. So it's possible to determine, for example, how much a psychology major from George Mason University earns compared to one from James Madison University ($28,195 vs. $24,711).

Paying for college is not just a one-year endeavor, of course. Students and their parents tend to pay close attention to how much debt they will take on when choosing a school, but less once enrolled.

As a reporter who has interviewed hundreds of undergraduates over the years, I have found that they are generally terrible at keeping track of how much debt they have. A 2014 study by economists at the Federal Reserve and Iowa State University found that nearly 10 percent of students underestimated their total debt by more than $10,000. That's one reason why three states — Florida, Indiana and Nebraska — require colleges and universities by law to provide detailed information about student debt and projected loan payments to students.

Economists often remind us that education debt is good debt. Taking on a student loan seems like a good investment, when placed next to the lower unemployment rate for college graduates and the lifetime payoff of a bachelor's degree. While a college degree might make good economic sense, one at any cost doesn't. Education debt may be good debt, but even too much of a good thing can hurt you.

Jeffrey J. Selingo is the author of There Is Life After College, about how today's graduates launch into their careers. He is former editor of the Chronicle of Higher Education. @jselingo