Quantification of the calorific content of microalgae is critical in studies of energy flow, trophic partitioning, plant/herbivore interactions in aquaculture and biomass production for biofuels. We investigated the calorific value and biochemical composition of Chlorella vulgaris at different phosphorus (P) concentrations (6.0 × 10−7, 2.3 × 10−6 and 2.3 × 10−4 mol L−1 P). As expected, the control (2.3 × 10−4 mol L−1 P) supported better growth than P limited treatments. Biomolecules like total carbohydrates and lipids accumulated under P limitation, which significantly correlated with high calorific values. Lipid class composition showed that triacylglycerols were the most accumulated under P limited conditions. The calorific value reported under control conditions (13.78 kJ g−1) was less than those obtained under P limitation (30.47–33.07 kJ g−1). The highest calorific value with less growth retardation was obtained at 2.3 × 10−6 mol L−1 P.