More than 8.5 million Americans are enrolled in income-based repayment plans that can spread out payments for their federal student loans for two decades or more. While the repayment plans lower the monthly payments of borrowers, these plans do not reduce the interest rates on student loans and can increase the total amount of interest borrowers pay over time. Borrowers with good income and credit are using another strategy: student loan refinancing. This means taking out a loan with a private lender, usually at a lower rate, to pay off the debt on the federal loan. Borrowers save more than $18,600 by reducing the rates on their student loans by an average of 1.7 percentage points through refinancing, according to Credible.com, a marketplace of online lenders.

It's not just for the HENRYs [high earners, not rich yet]. Stephen Dash founder and CEO of Credible

Law, pharmacy and medicine were the most common graduate degrees held by high-balance borrowers refinancing loans, according to Credible. These borrowers earned $126,192, on average, and refinanced loan balances averaging $150,511. You will need an excellent credit score to get the best deals with student loan refinancing. Eighty-four percent of high-balance borrowers who used Credible had credit scores of 740 or above when they refinanced. (Credit scores range from 300 to 850 and the average FICO score is 699.) "It's not just for the HENRYs [high earners, not rich yet], you can refinance your student loans with a credit score as low as 620 if they have a co-signer," said Stephen Dash, founder and CEO of Credible.

What you need to refinance