
Chapter 6: Cost of capital  
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Example: pre-tax and after-tax cost of debt 
 
A company has a bank loan of $100,000 on which it pays interest at 8%. The rate of 
tax on company profits is 25%. 
 
Gross interest on the loan each year is $8,000 and the pre-tax cost of the debt is 8%. 
This means that the company needs to make a profit of $8,000 each year before tax 
and interest in order to cover the interest cost of the debt. Tax relief on the interest is 
$2,000, which means that the tax charge for the company is reduced by $2,000 each 
year. The company therefore needs to make a profit after tax of $6,000 to cover the 
cost of the debt interest, and the after-tax cost of the debt is just 6%. The $6,000 after 
tax profit plus the reduction in the tax charge of $2,000 together provide the return 
of $8,000 that is needed to cover the cost of the debt interest. 
 
The after tax cost of debt is simply:  
  the pre-tax cost of debt  
  multiplied by a factor (1 – t) where t is the rate of tax on profits. 
1.2  WACC and capital investment appraisal 
One approach to the evaluation of capital investments by companies is that all their 
investment projects should be expected to provide a return equal to or in excess of the 
WACC. If all their investment projects earn a return in excess of the WACC, the 
company will earn sufficient returns overall to meet the cost of its capital and provide 
its investors with the returns they require. 
 
This principle is often applied in practice. The general rule is that when capital 
investment projects are evaluated using the NPV method, the cost of capital to be used 
is the WACC. This is on the assumption that the capital project will not alter the risk 
profile of the company’s investments and the risk with the new project is similar to the 
risks with the rest of the company’s business operations. 
 
The principle is often applied when the financing for a new capital investment changes 
the company’s WACC. On the assumption that the capital project will not alter the risk 
profile of the company’s investments, the NPV of the new project should be calculated 
using the new WACC that will exist after the project has been undertaken and financed. 
 
An alternative approach to the evaluation of capital investment projects, which does not 
use these assumptions, is the adjusted present value method or APV method. (This is 
explained in another chapter.)  
1.3  Comparing the cost of equity and the cost of debt 
For investors and for companies, the cost of their equity is always higher than the 
cost of their debt capital. This is because equity investment in a company is always 
more risky than investment in the debt capital of the same company. 
In addition, from a company’s perspective, the cost of debt is also reduced by the tax 
relief on interest payments. This makes debt finance even lower than the cost of equity. 
The effect of more debt capital, and higher financial gearing, on the WACC is 
considered in more detail later.