# How do I calculate the after-tax cost of debt?

Author:
Harold Averkamp, CPA, MBA

## Definition of After-Tax Cost of Debt

The after-tax cost of debt is the interest paid on the debt minus the income tax savings as the result of deducting the interest expense on the company’s income tax return.

## Example of After-Tax Cost of Debt

Let’s assume that a regular U.S. corporation has:

• A loan with an annual interest rate of 10%
• An incremental tax rate of 30% (combination of federal and state)

If the corporation has a loan of \$100,000 with an annual interest rate of 10%, the interest paid to the lender will be \$10,000 per year. This interest expense will reduce the corporation’s taxable income by \$10,000 thereby saving the corporation \$3,000 in income taxes (30% tax rate on \$10,000 reduction in taxable income).

The after-tax cost of the debt is computed as follows: \$10,000 paid to the lender minus \$3,000 of income tax savings equals a net cost of \$7,000 per year on the \$100,000 loan. This means the after-tax cost is 7% (\$7,000 divided by \$100,000) per year.

Using the example above, the after-tax interest rate can also be calculated. The formula for the after-tax rate is: the loan interest rate of 10% minus (30% tax savings on the 10% interest rate) = 10% minus 3% = 7%.

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