Now I encounter a question quite often from friends: "What exactly is WACC?" and why should we care. Honestly, investment decisions are not easy because it's not just about how much return you'll get, but also about considering the cost of the capital used.

Simply put, WACC is the average cost of capital that a company must pay to raise funds for business operations, whether it's bank loans or equity investments from shareholders. With this understanding, you can see why investors use this metric to evaluate whether a project is worth investing in.

Let's look at the structure first. A company's capital comes from two main sources: debt (loans) and equity. The cost of debt is the interest the company pays to the bank, while the cost of equity is the return that shareholders expect to receive.

The formula to calculate WACC is straightforward but requires several data points: WACC = (D/V)(Rd)(1-Tc) + (E/V)(Re), where D/V is the debt ratio, Rd is the cost of debt, Tc is the corporate tax rate, E/V is the equity ratio, and Re is the expected return.

Let's consider a real example. Suppose company XYZ has debt of 100 million baht (60%) and equity of 160 million baht (40%). The interest rate is 7%, corporate tax rate is 20%, and the expected return is 15%. Plugging in these values, the WACC is approximately 11.38%. This means that if the expected return (15%) is higher than WACC (11.38%), the project is considered worth investing in.

An important point to understand is that the lower the WACC, the better, because it indicates the company has a lower cost of raising capital. However, other factors should also be considered, such as the industry sector, project risk, and company policies. WACC alone should not be the sole criterion.

The optimal capital structure is to balance debt and equity in a way that minimizes WACC and maximizes shareholder value. Relying solely on equity results in a higher WACC, but incorporating debt can lower WACC because interest is tax-deductible.

But be cautious: WACC has limitations. It doesn't account for future changes, specific investment risks, and the calculation can be quite complex. Therefore, WACC is only an estimate and may have inaccuracies.

Using WACC effectively involves combining it with other metrics like NPV and IRR, and regularly updating the calculations to reflect changes in interest rates, debt levels, and economic conditions.

In summary, WACC is a crucial tool that helps investors understand the cost of capital and make better investment decisions. However, it should be used carefully and alongside other factors to ensure the best investment choices.