Six hundred and eighty-four male Ross 308 broiler chicks were used to test the null hypothesis that post hatching age between day 0 and 21 does not affect utilization of energy in meat and bone meal (MBM). There were 6 replicate cages in each of 12 treatments consisting of 3 test diets (0, 40, or 80 g MBM/kg diets) at 4 feeding ages post hatching (day 0 to 7, 6 to 11, 10 to 16, or 15 to 21 post hatching) for a total of 72 cages in a randomized complete block design. Birds were assigned to the 12 treatments on day 0, fed a standard starter diet until they were switched to the test diets on day 0, 6, 10, or 15, and the number of birds per cage for day 0 to 7, 6 to 11, 10 to 16, or 15 to 21 were 12, 10, 8, or 8, respectively. Excreta were collected during the last 3 days of each feeding age post hatching and ileal digesta on the last day of each age. There was no interaction between dietary MBM level and feeding age post hatching for any of the response criteria. Weight gain and gain-to-feed ratio improved linearly (P < 0.001) with increasing dietary MBM and, expectedly, there was an increase (P < 0.001) in weight gain and a reduction (P < 0.001) in gain-to-feed ratio with bird feeding age post hatching. Ileal digestible energy (IDE), apparent metabolizable energy (AME), and nitrogen-corrected AME (AMEn) of the diet linearly increased (P < 0.001) with increasing dietary MBM. There were linear increases in dietary IDE (P < 0.05), AME (P < 0.001), and AMEn (P < 0.001) with bird feeding age post hatching. The IDE, ME, and MEn of MBM were determined by the regression procedure. During day 0 to 7, 6 to 11, 10 to 16, or 15 to 21, energy values increased (P < 0.05) with age and the respective IDE of MBM were 2.852, 2.962, 2.927, or 2.959 kcal/g DM. Corresponding ME of MBM were 2.909, 3.125, 3.083, or 3.075 kcal/g DM and those of MEn were 2.687, 2.887, 2.839, or 2.845 kcal/g DM. These results show that energy values of MBM increase with age post hatching and suggest the same energy value of MBM should not be used in formulating diets of broiler chickens during the first 3 weeks post hatching.