JPMorgan Chase & Co. charges Mirella Tovar as much as 10.25 percent annual interest on her student loans – a rate as high as a credit card.

The 24-year-old aspiring graphic designer, the first in her family to go to college, is among millions of former students paying off high-interest loans to private lenders, among them JPMorgan, SLM Corp. and Discover Financial Services. In a good month, Tovar earns $730 as a part-time hostess in a pizza parlor, and most of that money goes toward her debt of $98,000.

Unlike the federal student-loan program, which lets consumers borrow at fixed rates directly from the government, these loans from at least 30 banks and other private lenders feature mostly variable rates that can be more than twice what some people pay in the U.S. program. With college costs spiraling, the marketing and interest rates of these loans are drawing increasing complaints from borrowers and regulators, who say teenage consumers often don’t understand their terms.

“It was like signing up for iTunes,” said Austin Bousley, 25, who applied on the Internet for a private loan from SLM, known as Sallie Mae, as a student at Suffolk University in Boston. Some of his loans, which he began taking out in 2006, carried rates as high as 9.25 percent. “The interest is accruing and accruing. I have a feeling I’ll be making payments forever.”

Loans from banks and other private lenders make up about 15 percent of the $1 trillion in outstanding student debt, according to an estimate by Mark Kantrowitz, who runs FinAid.org, a website about college grants and loans. About 2.9 million students have private loans, according to the most recent federal data analyzed by The Institute for College Access and Success, an Oakland, Calif.-based nonprofit group.

Now, with college costs continuing to soar, Discover and SLM are both working to expand their student-loan businesses.