The objective of this study was to evaluate the addition of fat to milk replacer as a supplemental energy source to reduce the negative effects of heat stress on growth and performance of dairy calves. Sixty calves (27 heifers and 33 bulls) housed in individual hutches were enrolled in a randomized block design from June 7 to Oct. 7, 2016 with THI ranging from 33 to 81. Calves were blocked by age and sex and randomly assigned to treatment: 1) milk replacer with no added fat (CON), 2) milk replacer with added fat when daily temperature exceeded 26°C (FTEMP), and 3) milk replacer with added fat for all study days (FALL). Calves were fed the same amount of milk replacer (26% crude protein, 18% fat, and 13% solids) twice daily following a step-up/step-down feeding strategy from 2 to 57 d of age. Fat was added at 1.2% of total reconstituted milk replacer for FTEMP and FALL increasing total solids to 14.2%. Calves had ad libitum access to a pelleted starter and water. Body weight, hip height, hip width, serum glucose, and serum nonesterified fatty acids were measured weekly. Intakes and health (body temperature, respiration, skin tent, eye recession, cough, nasal discharge, and fecal) were evaluated daily. Intake, growth, and feed efficiency data were averaged by week and analyzed using the GLIMMIX procedure of SAS. Health data were analyzed using logistic regression. The effect of feeding treatments was assessed using preplanned contrasts, comparing CON vs fat supplementation (FS = FTEMP + FALL) and FTEMP vs FALL. Average daily gain was 0.06 kg/d greater for FS from 2 to 43 d of age before weaning started. However, overall average daily gain (2 to 57 d) was not significant among treatments. Hip height and hip width also did not differ among treatments. Dry matter intake was increased for FS resulting in greater overall feed efficiency for CON-fed calves. Serum nonesterified fatty acids were greater for FS than CON. Calves fed FS had higher respiration rates with FALL being greater than FTEMP. All other health parameters were similar among treatments. The results of this study indicate that calves did not benefit from fat supplementation during the summer months.