The weight of debt is an important component of the WACC formula. In estimating the weight of debt, would you consider short-term debt and the current portion of long-term debt as debt? What about notes payable and accounts payable?
Yes, short-term debt and the current portion of long-term debt are included in debt when computing the weight of debt.
All interest-bearing liabilities are included in debt when computing the weight of debt. The reason is that you are estimating the cost of capital and so want to figure out the proportion of capital funded by debt. Since capital providers want a return on their capital proportionate to the risk taken, they will demand a fee (an interest) for their capital. Therefore, interest is considered the indicator of the liabilities to be included in debt.