While computing the cost of equity using the formula , rs=D1P0+grs=D1P0+g, we do not make any adjustment to express the cost of equity on an after-tax basis whereas while computing the cost of debt, a...

While computing the cost of equity using the formula , rs=D1P0+grs=D1P0+g, we do not make any adjustment to express the cost of equity on an after-tax basis whereas while computing the cost of debt, a tax adjustment is required to arrive at after-tax cost of debt. Why is this so?