Medicare must pay interest on clean claims if payment is not made within the applicable number of calendar days (i.e., 30 days) after the date of receipt. The applicable number of days is also known as the payment ceiling. The new rate of 2.375 percent is in effect through December 31, 2017. The interest rate is determined by the applicable rate on the day of payment. This rate is determined by the Treasury Department on a six-month basis, effective every January and July 1. Providers may access the Treasury Department web page https://www.fiscal.treasury.gov/fsservices/gov/pmt/promptPayment/rates.htm for the correct rate. The interest period begins on the day after payment is due and ends on the day of payment.