Cost of Capital Boeing’s weighted-average cost of capital (WACC) could be estimated using the following well-known formula: WACC = (percent Debt)(rd)(1 – tc) + (percent Equity)(re) where: rd = Pretax cost of debt capital tc = Marginal effective corporate tax rate percent Debt = Proportion of debt in a market-value capital structure re = Cost of equity capital percent Equity = Proportion of equity in a market-value capital structure