Abstract: An experiment was conducted to determine the effect of dietary Ca levels on True Metabolizable Energy (TME) and TME with nitrogen correction (TMEn) values of 3 fat sources (cotton seed oil, animal fat and a 50:50 mixture). The fats were each added at the level of 0, 3, 6 and 9% to 2 basal low and high Ca content diets. The true metabolizable energy of experimental diets was determined using precision fed rooster assay method. The TME and TMEn of 3 fat sources were obtained through regression and extrapolation to 100% fat replacement in basal diets. The addition of Ca carbonate to the zero added fat diet significantly (p<0.05) reduced the TMEn of diet (3348 vs. 3294 kcal kg-1). The true metabolizable energy of animal fat was significantly (p<0.05) lower than that of cotton seed oil (8619 vs. 9974 kcal kg-1). However, the TMEn of fat and oil mixture was similar to that of oil value (9974 vs. 9915 kcal kg-1). The TMEn of fat decreased as the level of fat increased (p<0.01) when it was calculated by the difference method. Addition of Ca carbonate to the diets contained any sources of fat significantly (p<0.05) reduced the TMEn value of fat. The metabolizable energy of fat linearly (p<0.05) reduced in response to increase in dietary fat levels as determined by difference method.