In the residual income model, the intrinsic value of a share of common stock is the sum of book value per share and the present value of expected future pershare residual income. In the residual income model, the equivalent mathematical expressions for intrinsic value of a common stock are V0=B0+∑t=1∞RIt(1+r)t=B0+∑t=1∞Et−rBt−1(1+r)t=B0+∑t=1∞(ROEt−r)Bt−1(1+r)t 
Residual income is calculated as net income less a charge for the cost of capital. The charge is known as the equity charge and is calculated as the value of equity capital multiplied by the cost of equity or the required rate of return on equity. Given the opportunity cost of equity, a company can have positive net income but negative residual income.