‘Tis the season for caps and gowns and college diplomas. For a lot of new graduates it’s also time to start paying back those student loans. If you’re wondering how long that might take, it depends on your profession.

Want to pay off your student loans in about 6 years? Get a degree in advertising or marketing. But according to BankRate.com, if you become a librarian, plan on shelling out monthly payments for over two decades.

BankRate analyst Jessica Patel says lenders won’t really give you that much time.

“But it kind of gives you an idea of how long it would actually take if you’re just paying it for a return on investment,” she says. Patel says the new numbers assume you put 10 percent of your yearly salary toward your loan.

So students should factor in earning potential when choosing a career path — but that shouldn’t be the only factor.

“If you don’t like what you do and what you study, you won’t be any good at it,” says Tony Carnevale, Director of the Center for Education and the Workforce at Georgetown University. “We have lots of data that tells us that.”

He says it doesn’t hurt to plan ahead, especially if your plan is to get rich. In that case, don’t become a marriage counselor. BankRate.com says that degree has the worst ROI, with a payoff period of 35 years.

Sources: Bureau of Labor Statistics, National Center for Education Statistics, FinAid.org.