On January 21, 2015, a new interest rate of 10.5% for Medicare overpayments and underpayments became effective. The new rate is lower than the previous rate of 10.75% that has been in place since October 20, 2014.
The federal regulations provide for the charging and payment of interest to Medicare providers for overpayments and underpayments, which interest is assessed on delinquent debts. This interest rate is certified quarterly by the Department of the Treasury and is based on current consumer interest rate data. Since 2001, the interest rate has ranged from as high as 14.125% in 2001, to as low as 10.125% in early 2014.
The CMS transmittal is available here.