This study aimed to evaluate the impact of branched-chain amino acid (BCAA) levels above the recommended values on the performance of broilers fed reduced crude protein (RCP) diets with different energy densities. A Box-Behnken design was used comprising of three factors: net energy (NE, 9.0; 9.7 or 10.4 MJ/kg), BCAA (0%, 20% or 40% above the recommended requirements), and crude protein (CP, 15%, 17% or 19%). Thus, 13 wheat-barley-based diets were formulated in three forms: mash, crumbles, or a combination of mash and crumbles. A total of 1092 as-hatched Cobb 500 Elevating branched-chain amino acids beyond the recommended requirements may have a negative impact on the performance of broilers fed reduced crude protein diets broilers was used, with 7 replicates per treatment and 12 birds per replicate. Diets were offered as a common starter diet (d0 – 8), a common grower diet (d9 – 18), and test finisher diets (d19 – 35). The growth performance was evaluated by weighing the birds and feeds on d19, 28 and 35. Data were statistically analysed utilising the response surface of the JMP fit Linear Regression Models. The male percentage was used as a covariate, and the feed form was incorporated in the model to account for its impact. The study presents the results from d19 – 35. The significant interactions between factors (CP × NE and CP × BCAA) were fixed at 0% excess BCAA and 9.7 MJ/kg NE, respectively. The results revealed significant interactions on weight gain (WG) between CP and NE (P < 0.001) and between CP and BCAA (P < 0.0001). The CP × NE interaction indicated that birds fed diets with high NE densities had greater WG when they were fed high crude protein (HCP) diets. When fed RCP diets, there was no difference in WG between birds fed low and high NE density diets. The CP × BCAA interaction showed that birds offered diets containing high levels of BCAA showed a decrease in WG when they were fed RCP diets, as compared to those supplemented with 0% additional BCAA. In diets with HCP however, there was no effect on WG by the BCAA levels. The interactions on feed intake (FI) were also noted (CP × NE, P < 0.01 and CP × BCAA, P < 0.0001) showing a similar pattern as WG. A CP × BCAA interaction (P < 0.0001) was observed in relation to feed conversion ratio (FCR). This interaction indicated that 4% additional BCAA supplementation resulted in higher FCR in RCP-diets compared to 0% additional BCAA, while BCAA levels did not affect FCR in HCP diets.