The tokamak as a magnetic confinement device has evolved over the years and is seen globally as a prominent candidate for a thermonuclear fusion reactor. However, obtaining electrical power from controlled fusion still faces hard technological challenges. Apart from the physics of plasma, fusion research is now more about the engineering problem such as the blanket design, superconductivity, radiation damage, tritium breeding and power management. Evaluation of proper power balance is highly essential for deciding reactor cost and economic power generation. The paper goes beyond Lawson’s criterion and analyzes the energy flow in a tokamak fusion power plant which is more relevant to the real situation. Firstly, two primary figures of merit, the fusion gain \(\left( Q \right){ }\) and Lawson triple product \(\left( {n\tau T} \right){ }\) were calculated for power break-even and net electrical power production. Then, sensitivity of key reactor parameters such as the re-circulating power fraction, overall pant efficiency were examined. The calculations performed also takes into consideration certain practical conditions like tritium breeding in blankets, fuel dilution due to impurities and standard plasma profiles. The investigation reveals that \(Q{ }\) greater than around 30 is desirable for an economical tokamak operation.