Interest Tax Shield

When a company pays interest on its debt, that interest reduces taxable income. If a company has $100M in interest expense and a 25% tax rate, it saves $25M in taxes that it would otherwise owe. This $25M is the annual tax shield. The tax shield effectively subsidizes the cost of debt, which is why the after-tax cost of debt equals the pre-tax rate multiplied by (1 - tax rate).

In the WACC approach, the tax shield is captured by using the after-tax cost of debt in the weighted average calculation. In the Adjusted Present Value (APV) method, the firm is first valued as if it were all-equity, and then the present value of future tax shields is added separately. APV is particularly useful when the capital structure is expected to change significantly over time, as in LBO scenarios where debt is paid down rapidly.

LBOs rely heavily on the interest tax shield to enhance equity returns. By loading a target company with debt, the PE sponsor reduces the company's tax bill, effectively transferring value from the government to debt and equity holders. As the company generates cash flow and pays down debt, the tax shield declines over time. Modeling the tax shield year by year is important for accurately projecting LBO returns.

The tax shield only provides value if the company has sufficient taxable income to utilize the deduction. Companies with net operating losses or very low profitability may not benefit from additional interest deductions. Tax law changes, such as limitations on interest deductibility under Section 163(j), can cap the tax shield at 30% of adjusted taxable income. Excessive debt also increases financial distress risk, which can offset the tax shield benefit.