A power consumption calculating apparatus includes a receiving unit, a specifying unit, a determining unit, an average calculating unit, an estimating unit, and a power consumption calculating unit. The receiving unit receives data of a target circuit. The specifying unit specifies a sequential circuit in the circuit. The determining unit, by developing a sequential circuit to a combinational circuit, determines a clock cycle to be input into the combinational circuit. The average calculating unit calculates the average number of transition after the number of transition of 2N-clock cycle is calculated. The estimating unit estimates the estimated number of transition. And the power consumption calculating unit calculates the maximum power consumption.