Earnest, a lending startup that refinances student loans and originates personal loans, thinks it can help.

Loan-refinancing may not seem like the sexiest corner of fintech, but it has very recently become very hot: SoFi, which provides student loans, mortgages and other kinds of loans, scored a $1 billion investment from Softbank in September.

The tool allows an Earnest customer to select any monthly payment on a loan and change it on the fly; the interest rate will adjust to match.

“$1,000 a month might mean a 10-and-a-half year loan, not a 10-year loan or a 15-year loan,” Beryl says.

Now Earnest is growing so fast that it originated 50 times as many loans in 2015 as it did in 2014.

More than 40 million Americans have at least one student loan.

As Yahoo Finance’s Mandi Woodruff has warned, refinancing a student loan can be the wrong move in some cases.