The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure the solar radiation reflected by the earth and thermal radiation emitted by the earth. Four CERES instruments are already in service; two aboard the Terra spacecraft, launched in 1999; and two aboard the Aqua spacecraft, launched in 2002. A fifth instrument, flight model 5 (FM5), launched in October 2011 aboard the NPP satellite, began taking radiance measurements on January 27th, 2012. The CERES FM5 instrument uses three scanning thermistor bolometers to make broadband radiance measurements in the shortwave (0.3 - 5.0 micrometers), total (0.3 - <100 micrometers) and water vapor window (8 - 12 micrometer) regions. An internal calibration module (ICM) used for in-flight calibration is built into the CERES instrument package consisting of an anodized aluminum blackbody source for calibrating the total and window sensors, and a shortwave internal calibration source (SWICS) for the shortwave sensor. The calibration sources are used to define shifts or drifts in the sensor response over the life of the mission. In order to better understand the sensors adaptation to the space environment, daily internal calibrations were conducted on all three channels for the first week after opening the instrument’s main covers. Over the next month, the frequency of internal calibrations was reduced to the standard mission schedule of three total and window channel calibrations per week and one shortwave channel calibration per week. This paper presents the results of FM5 on-orbit internal calibrations, discusses any ground to flight changes, and describes trends in the calibration data.