The cost of capital is the weighted average of the cost of debt and equity. It is a factor in deciding which financing path to follow.
The cost of capital is calculated using the weighted average cost of capital (WACC) formula: WACC = E/V * Re + D/V * Rd * (1-T)
, where E is the market value of equity, V is the market value of total capital, Re is the cost of equity, D is the market value of debt, Rd is the cost of debt and T is the tax rate.
The cost of capital includes both debt and equity.