After-Tax Cost of Debt
5 minutes
5 Questions
The after-tax cost of debt is the effective interest rate a company pays on its borrowings once the tax deductibility of interest expense is taken into account. In the CTP framework for Capital Structure and Long-Term Capital, it is a critical input because debt is typically the cheapest component of a firm's capital and its true cost is reduced by the tax shield that interest payments create. The formula is straightforward: After-Tax Cost of Debt = Pre-Tax Cost of Debt × (1 − Marginal Tax Rate). The pre-tax cost of debt is usually the yield to maturity on the firm's existing long-term bonds or the rate at which it could issue new debt today, not the historical coupon rate. The marginal tax rate is used because it reflects the tax savings on the next dollar of interest paid. For example, if a company can borrow at 6% and faces a 25% marginal tax rate, its after-tax cost of debt is 6% × (1 − 0.25) = 4.5%. The 1.5% difference represents the government effectively subsidizing part of the interest expense through lower taxable income. This measure matters for several reasons. First, it feeds directly into the Weighted Average Cost of Capital (WACC), which treasurers use as the hurdle rate for evaluating capital projects and acquisitions. Second, it illustrates why firms are incentivized to include debt in their capital structure, consistent with the trade-off theory, where the tax advantage of debt is balanced against rising financial distress and agency costs as leverage increases. Third, it highlights sensitivity to tax policy: a lower statutory rate raises the after-tax cost of debt and may shift optimal leverage. Treasury professionals should also note limitations. The tax shield only has value if the firm generates sufficient taxable income to use the deduction, and interest deductibility may be capped under certain tax regulations. Flotation costs on new issues should also be considered when estimating the true cost of raising long-term debt.
After-Tax Cost of Debt: A Complete CTP Study Guide (Capital Structure and Long-Term Capital)
1. Why the After-Tax Cost of Debt Matters
The after-tax cost of debt is one of the most frequently tested calculations in the AFP Certified Treasury Professional (CTP) exam's capital structure and long-term capital domain. It sits at the heart of three decisions a treasury professional makes constantly:
• Financing decisions – Should the firm raise capital through debt or equity? Debt is almost always cheaper than equity, and the tax deductibility of interest makes it cheaper still. Understanding the true, after-tax cost lets treasury compare apples to apples.
• Capital budgeting – The after-tax cost of debt is a direct input into the Weighted Average Cost of Capital (WACC), which is the discount rate used to evaluate projects via NPV and IRR. An error in the after-tax cost of debt flows straight into every project valuation the company performs.
• Capital structure optimization – Firms seek the mix of debt and equity that minimizes WACC and maximizes firm value. Because interest is tax-deductible while dividends are not, debt carries a tax shield that is a central reason leverage can add value (up to the point where financial distress costs outweigh the benefit).
For the exam, this topic is important because it is highly calculable: examiners can give you a few numbers and expect a precise answer. It also tests whether you understand the conceptual difference between the pre-tax yield that lenders demand and the after-tax cost that the company actually bears.
2. What the After-Tax Cost of Debt Is
The cost of debt is the effective rate a company pays on its borrowed funds. Because interest expense is deductible in computing taxable income (subject to limitations), each dollar of interest reduces the company's tax bill. The government, in effect, subsidizes part of the interest cost. The after-tax cost of debt is therefore the pre-tax cost reduced by the tax savings generated by the interest deduction.
Core formula:
After-Tax Cost of Debt = Pre-Tax Cost of Debt × (1 − Marginal Tax Rate)
or, in symbols: Kd(after-tax) = Kd × (1 − T)
where Kd is the pre-tax cost of debt (usually the yield to maturity on new debt) and T is the firm's marginal corporate tax rate.
The tax shield is the portion of interest that the tax deduction saves: Interest Tax Shield = Interest Expense × T, or expressed as a rate, Kd × T.
3. How It Works – Step by Step
Step 1: Identify the pre-tax cost of debt (Kd).
The theoretically correct pre-tax cost is the yield to maturity (YTM) on new debt the firm could issue today, not the coupon rate on old bonds and not the historical interest rate. On the exam, the pre-tax cost may be given directly as 'the company can borrow at 7%,' or as 'the yield to maturity on the firm's bonds is 7%,' or you may need to infer it. If a bond is trading at par, the coupon rate equals the YTM. If the bond trades at a premium, YTM is below the coupon; at a discount, YTM is above the coupon.
Step 2: Identify the marginal tax rate (T).
Use the marginal rate (the rate applied to the next dollar of income), not the average or effective rate, unless the question says otherwise. The marginal rate is what determines how much tax a deduction actually saves. If both federal and state rates are given, use the combined rate the question specifies.
Step 3: Apply the formula.
Multiply the pre-tax cost by (1 − T).
Worked Example 1 – Basic
A company can issue new 10-year bonds at a yield of 8%. Its marginal tax rate is 25%.
After-tax cost of debt = 8% × (1 − 0.25) = 8% × 0.75 = 6.0%
Tax shield on the rate = 8% × 0.25 = 2.0 percentage points.
Worked Example 2 – Dollar Terms
A firm borrows $10,000,000 at 6% interest. Marginal tax rate is 21%.
Annual interest = $600,000
Tax savings = $600,000 × 0.21 = $126,000
After-tax interest = $600,000 − $126,000 = $474,000
After-tax cost = $474,000 / $10,000,000 = 4.74% (which equals 6% × 0.79).
Worked Example 3 – Bonds at Par
A firm's outstanding bonds carry a 7.5% coupon and trade at par. Tax rate 30%.
Because the bonds trade at par, YTM = coupon = 7.5%.
After-tax cost = 7.5% × 0.70 = 5.25%
Worked Example 4 – Using Price to Find YTM
A bond with a $1,000 face value, 6% annual coupon, 10 years to maturity, sells for $920. Tax rate 25%.
Approximate YTM = [Coupon + (Face − Price)/n] / [(Face + Price)/2] = [60 + (1,000 − 920)/10] / [(1,000 + 920)/2] = (60 + 8) / 960 = 7.08%
After-tax cost ≈ 7.08% × 0.75 = 5.31%
(A financial calculator gives YTM ≈ 7.13%, so after-tax ≈ 5.35%. Choose the closest answer.)
Worked Example 5 – Feeding WACC
Capital structure: 40% debt, 60% equity. Pre-tax cost of debt 8%, tax rate 25%, cost of equity 12%.
After-tax Kd = 8% × 0.75 = 6%
WACC = 0.40 × 6% + 0.60 × 12% = 2.4% + 7.2% = 9.6%
Note that equity is never tax-adjusted because dividends are not deductible.
4. Important Nuances and Refinements
• Flotation costs. If new debt is issued with underwriting fees, the firm receives less than face value, which raises the effective pre-tax cost. Adjust the net proceeds before computing yield, then apply (1 − T). Example: 8% coupon bond sold at par with 2% flotation costs → net proceeds $980 per $1,000 → pre-tax cost ≈ 80/980 = 8.16% → after-tax ≈ 8.16% × 0.75 = 6.12%.
• Marginal vs. effective tax rate. Always use marginal unless told otherwise. A firm with large losses and a zero marginal tax rate gets no tax shield; its after-tax cost of debt equals its pre-tax cost.
• Interest deductibility limits. Under U.S. tax law (IRC Section 163(j)), business interest deductions are capped at a percentage of adjusted taxable income (generally 30%). If a firm's interest exceeds the cap, the excess provides no current tax shield, so the effective after-tax cost on the marginal debt is higher than the simple formula suggests. The CTP exam may test the concept that tax shields are only valuable if the firm has sufficient taxable income.
• Market vs. book values. For WACC weights and for determining Kd, use market values and current yields, not book values or historical coupon rates.
• Debt vs. preferred vs. equity. Only debt interest is tax-deductible. Preferred dividends and common dividends are paid from after-tax income, so their costs are not adjusted. This is a classic distractor.
• Leases. Lease payments (or the interest component) are often deductible, so the after-tax cost of lease financing is computed similarly; lease-versus-buy analyses discount cash flows at the after-tax cost of debt.
• Why debt is cheaper than equity. Debt holders have priority claims and contractual payments, so they bear less risk and demand lower returns than equity holders. The tax shield widens that gap further. However, more debt raises financial risk and eventually increases both the cost of debt and cost of equity (trade-off theory).
5. How to Answer Exam Questions on After-Tax Cost of Debt
Most CTP questions on this topic fall into four patterns:
Pattern A – Direct calculation. Given a pre-tax rate and a tax rate, compute the after-tax cost. Simply multiply by (1 − T). Watch for percentages given as decimals or whole numbers.
Pattern B – Reverse calculation. Given the after-tax cost and the tax rate, find the pre-tax cost: Kd = After-tax cost / (1 − T). Example: after-tax cost 4.5%, T = 25% → pre-tax = 4.5% / 0.75 = 6.0%. Or given pre-tax and after-tax costs, solve for the tax rate: T = 1 − (After-tax / Pre-tax).
Pattern C – Embedded in WACC. You must compute the after-tax cost of debt as one step toward WACC. Do the tax adjustment on debt only, then weight.
Pattern D – Conceptual. Which statement is true about the after-tax cost of debt? Typical correct statements: it is lower than the pre-tax cost when the firm pays taxes; it is based on the yield on new debt rather than the coupon on old debt; it uses the marginal tax rate; it falls as the tax rate rises; it is the relevant cost for WACC.
Step-by-step approach in the exam:
1. Read the question and underline the pre-tax rate, the tax rate, and whether the question asks for pre-tax, after-tax, or WACC.
2. Confirm the rate given is the cost of debt, not the cost of equity or preferred.
3. Check for bond price information that implies YTM differs from coupon.
4. Check for flotation costs.
5. Compute (1 − T) first, then multiply.
6. Sanity-check: the after-tax cost must be lower than the pre-tax cost (unless T = 0), and should be below the cost of equity.
6. Exam Tips: Answering Questions on After-Tax Cost of Debt
• Memorize the formula cold: Kd × (1 − T). It is short, but under time pressure candidates sometimes multiply by T instead of (1 − T). Multiplying by T gives the tax shield, not the after-tax cost.
• Never tax-adjust equity or preferred stock. If a WACC question has three components, only the debt component is multiplied by (1 − T).
• Use the marginal tax rate. If the question offers both an effective rate and a marginal rate, the marginal rate is correct for the cost of capital.
• Use the current yield to maturity on new debt, not the coupon rate on existing debt or the rate paid years ago. If the bond trades at par, coupon = YTM, which is often how examiners simplify.
• Watch for a zero or low tax rate. A firm with net operating losses or in a tax-exempt structure may have no tax shield; the after-tax cost then equals the pre-tax cost.
• Read units carefully. A tax rate of 25 means 0.25 in the formula. A pre-tax cost of 0.08 and a tax rate of 25% gives 0.06, or 6%.
• Reverse-engineer when needed. If given after-tax and asked for pre-tax, divide by (1 − T). Do not multiply.
• Higher tax rate = lower after-tax cost of debt. Conceptual questions often test this inverse relationship. A corporate tax cut (like the 2017 reduction from 35% to 21%) raises the after-tax cost of debt and reduces the relative attractiveness of leverage.
• Flotation costs raise the cost of debt. Compute the yield on net proceeds first, then apply the tax adjustment.
• Sanity-check answer choices. Eliminate any option higher than the pre-tax rate (impossible with a positive tax rate) and any option equal to the pre-tax rate multiplied by T alone.
• Link to WACC and capital structure theory. Be ready to explain that the tax deductibility of interest is the primary reason debt lowers WACC (Modigliani-Miller with taxes), and that the benefit is offset at high leverage by financial distress and agency costs.
• Manage your time. These are typically one-step or two-step calculations. Do them quickly and accurately, then move on; do not over-think a question that simply wants Kd × (1 − T).
7. Quick Practice Questions
Q1. A company's bonds yield 9%. Its marginal tax rate is 30%. What is the after-tax cost of debt?
Answer: 9% × 0.70 = 6.3%
Q2. A firm's after-tax cost of debt is 5.6% and its marginal tax rate is 20%. What is the pre-tax cost?
Answer: 5.6% / 0.80 = 7.0%
Q3. A firm has 30% debt at a pre-tax cost of 6%, 10% preferred stock costing 8%, and 60% common equity costing 11%. Tax rate 25%. What is WACC?
Answer: Debt after-tax = 6% × 0.75 = 4.5%. WACC = 0.30 × 4.5% + 0.10 × 8% + 0.60 × 11% = 1.35% + 0.80% + 6.60% = 8.75% (note preferred is not tax-adjusted).
Q4. Which of the following would increase a firm's after-tax cost of debt? (a) An increase in the corporate tax rate; (b) A decrease in the corporate tax rate; (c) A credit rating upgrade; (d) A decline in market interest rates.
Answer: (b). A lower tax rate shrinks the tax shield, raising the after-tax cost. Options (c) and (d) lower the pre-tax cost, and (a) lowers the after-tax cost.
Q5. A firm has substantial net operating loss carryforwards and expects to pay no income tax for several years. Its bonds yield 7%. What is its effective after-tax cost of debt?
Answer: 7%. With no taxable income, there is no current tax shield, so the after-tax cost equals the pre-tax cost.
8. Summary
The after-tax cost of debt measures what borrowing truly costs a company after accounting for the tax deductibility of interest. It is calculated as the pre-tax yield on new debt multiplied by (1 − marginal tax rate). It is always lower than the pre-tax cost for a tax-paying firm, it is the only component of WACC that receives a tax adjustment, and it rises when tax rates fall. For the CTP exam, master the formula, know when to use YTM versus coupon, remember to use the marginal tax rate, never tax-adjust equity or preferred stock, and sanity-check that your answer is below the pre-tax rate. With these habits, after-tax cost of debt questions become reliable points on exam day.
The after-tax cost of debt is one of the most frequently tested calculations in the AFP Certified Treasury Professional (CTP) exam's capital structure and long-term capital domain. It sits at the heart of three decisions a treasury professional makes constantly:
• Financing decisions – Should the firm raise capital through debt or equity? Debt is almost always cheaper than equity, and the tax deductibility of interest makes it cheaper still. Understanding the true, after-tax cost lets treasury compare apples to apples.
• Capital budgeting – The after-tax cost of debt is a direct input into the Weighted Average Cost of Capital (WACC), which is the discount rate used to evaluate projects via NPV and IRR. An error in the after-tax cost of debt flows straight into every project valuation the company performs.
• Capital structure optimization – Firms seek the mix of debt and equity that minimizes WACC and maximizes firm value. Because interest is tax-deductible while dividends are not, debt carries a tax shield that is a central reason leverage can add value (up to the point where financial distress costs outweigh the benefit).
For the exam, this topic is important because it is highly calculable: examiners can give you a few numbers and expect a precise answer. It also tests whether you understand the conceptual difference between the pre-tax yield that lenders demand and the after-tax cost that the company actually bears.
2. What the After-Tax Cost of Debt Is
The cost of debt is the effective rate a company pays on its borrowed funds. Because interest expense is deductible in computing taxable income (subject to limitations), each dollar of interest reduces the company's tax bill. The government, in effect, subsidizes part of the interest cost. The after-tax cost of debt is therefore the pre-tax cost reduced by the tax savings generated by the interest deduction.
Core formula:
After-Tax Cost of Debt = Pre-Tax Cost of Debt × (1 − Marginal Tax Rate)
or, in symbols: Kd(after-tax) = Kd × (1 − T)
where Kd is the pre-tax cost of debt (usually the yield to maturity on new debt) and T is the firm's marginal corporate tax rate.
The tax shield is the portion of interest that the tax deduction saves: Interest Tax Shield = Interest Expense × T, or expressed as a rate, Kd × T.
3. How It Works – Step by Step
Step 1: Identify the pre-tax cost of debt (Kd).
The theoretically correct pre-tax cost is the yield to maturity (YTM) on new debt the firm could issue today, not the coupon rate on old bonds and not the historical interest rate. On the exam, the pre-tax cost may be given directly as 'the company can borrow at 7%,' or as 'the yield to maturity on the firm's bonds is 7%,' or you may need to infer it. If a bond is trading at par, the coupon rate equals the YTM. If the bond trades at a premium, YTM is below the coupon; at a discount, YTM is above the coupon.
Step 2: Identify the marginal tax rate (T).
Use the marginal rate (the rate applied to the next dollar of income), not the average or effective rate, unless the question says otherwise. The marginal rate is what determines how much tax a deduction actually saves. If both federal and state rates are given, use the combined rate the question specifies.
Step 3: Apply the formula.
Multiply the pre-tax cost by (1 − T).
Worked Example 1 – Basic
A company can issue new 10-year bonds at a yield of 8%. Its marginal tax rate is 25%.
After-tax cost of debt = 8% × (1 − 0.25) = 8% × 0.75 = 6.0%
Tax shield on the rate = 8% × 0.25 = 2.0 percentage points.
Worked Example 2 – Dollar Terms
A firm borrows $10,000,000 at 6% interest. Marginal tax rate is 21%.
Annual interest = $600,000
Tax savings = $600,000 × 0.21 = $126,000
After-tax interest = $600,000 − $126,000 = $474,000
After-tax cost = $474,000 / $10,000,000 = 4.74% (which equals 6% × 0.79).
Worked Example 3 – Bonds at Par
A firm's outstanding bonds carry a 7.5% coupon and trade at par. Tax rate 30%.
Because the bonds trade at par, YTM = coupon = 7.5%.
After-tax cost = 7.5% × 0.70 = 5.25%
Worked Example 4 – Using Price to Find YTM
A bond with a $1,000 face value, 6% annual coupon, 10 years to maturity, sells for $920. Tax rate 25%.
Approximate YTM = [Coupon + (Face − Price)/n] / [(Face + Price)/2] = [60 + (1,000 − 920)/10] / [(1,000 + 920)/2] = (60 + 8) / 960 = 7.08%
After-tax cost ≈ 7.08% × 0.75 = 5.31%
(A financial calculator gives YTM ≈ 7.13%, so after-tax ≈ 5.35%. Choose the closest answer.)
Worked Example 5 – Feeding WACC
Capital structure: 40% debt, 60% equity. Pre-tax cost of debt 8%, tax rate 25%, cost of equity 12%.
After-tax Kd = 8% × 0.75 = 6%
WACC = 0.40 × 6% + 0.60 × 12% = 2.4% + 7.2% = 9.6%
Note that equity is never tax-adjusted because dividends are not deductible.
4. Important Nuances and Refinements
• Flotation costs. If new debt is issued with underwriting fees, the firm receives less than face value, which raises the effective pre-tax cost. Adjust the net proceeds before computing yield, then apply (1 − T). Example: 8% coupon bond sold at par with 2% flotation costs → net proceeds $980 per $1,000 → pre-tax cost ≈ 80/980 = 8.16% → after-tax ≈ 8.16% × 0.75 = 6.12%.
• Marginal vs. effective tax rate. Always use marginal unless told otherwise. A firm with large losses and a zero marginal tax rate gets no tax shield; its after-tax cost of debt equals its pre-tax cost.
• Interest deductibility limits. Under U.S. tax law (IRC Section 163(j)), business interest deductions are capped at a percentage of adjusted taxable income (generally 30%). If a firm's interest exceeds the cap, the excess provides no current tax shield, so the effective after-tax cost on the marginal debt is higher than the simple formula suggests. The CTP exam may test the concept that tax shields are only valuable if the firm has sufficient taxable income.
• Market vs. book values. For WACC weights and for determining Kd, use market values and current yields, not book values or historical coupon rates.
• Debt vs. preferred vs. equity. Only debt interest is tax-deductible. Preferred dividends and common dividends are paid from after-tax income, so their costs are not adjusted. This is a classic distractor.
• Leases. Lease payments (or the interest component) are often deductible, so the after-tax cost of lease financing is computed similarly; lease-versus-buy analyses discount cash flows at the after-tax cost of debt.
• Why debt is cheaper than equity. Debt holders have priority claims and contractual payments, so they bear less risk and demand lower returns than equity holders. The tax shield widens that gap further. However, more debt raises financial risk and eventually increases both the cost of debt and cost of equity (trade-off theory).
5. How to Answer Exam Questions on After-Tax Cost of Debt
Most CTP questions on this topic fall into four patterns:
Pattern A – Direct calculation. Given a pre-tax rate and a tax rate, compute the after-tax cost. Simply multiply by (1 − T). Watch for percentages given as decimals or whole numbers.
Pattern B – Reverse calculation. Given the after-tax cost and the tax rate, find the pre-tax cost: Kd = After-tax cost / (1 − T). Example: after-tax cost 4.5%, T = 25% → pre-tax = 4.5% / 0.75 = 6.0%. Or given pre-tax and after-tax costs, solve for the tax rate: T = 1 − (After-tax / Pre-tax).
Pattern C – Embedded in WACC. You must compute the after-tax cost of debt as one step toward WACC. Do the tax adjustment on debt only, then weight.
Pattern D – Conceptual. Which statement is true about the after-tax cost of debt? Typical correct statements: it is lower than the pre-tax cost when the firm pays taxes; it is based on the yield on new debt rather than the coupon on old debt; it uses the marginal tax rate; it falls as the tax rate rises; it is the relevant cost for WACC.
Step-by-step approach in the exam:
1. Read the question and underline the pre-tax rate, the tax rate, and whether the question asks for pre-tax, after-tax, or WACC.
2. Confirm the rate given is the cost of debt, not the cost of equity or preferred.
3. Check for bond price information that implies YTM differs from coupon.
4. Check for flotation costs.
5. Compute (1 − T) first, then multiply.
6. Sanity-check: the after-tax cost must be lower than the pre-tax cost (unless T = 0), and should be below the cost of equity.
6. Exam Tips: Answering Questions on After-Tax Cost of Debt
• Memorize the formula cold: Kd × (1 − T). It is short, but under time pressure candidates sometimes multiply by T instead of (1 − T). Multiplying by T gives the tax shield, not the after-tax cost.
• Never tax-adjust equity or preferred stock. If a WACC question has three components, only the debt component is multiplied by (1 − T).
• Use the marginal tax rate. If the question offers both an effective rate and a marginal rate, the marginal rate is correct for the cost of capital.
• Use the current yield to maturity on new debt, not the coupon rate on existing debt or the rate paid years ago. If the bond trades at par, coupon = YTM, which is often how examiners simplify.
• Watch for a zero or low tax rate. A firm with net operating losses or in a tax-exempt structure may have no tax shield; the after-tax cost then equals the pre-tax cost.
• Read units carefully. A tax rate of 25 means 0.25 in the formula. A pre-tax cost of 0.08 and a tax rate of 25% gives 0.06, or 6%.
• Reverse-engineer when needed. If given after-tax and asked for pre-tax, divide by (1 − T). Do not multiply.
• Higher tax rate = lower after-tax cost of debt. Conceptual questions often test this inverse relationship. A corporate tax cut (like the 2017 reduction from 35% to 21%) raises the after-tax cost of debt and reduces the relative attractiveness of leverage.
• Flotation costs raise the cost of debt. Compute the yield on net proceeds first, then apply the tax adjustment.
• Sanity-check answer choices. Eliminate any option higher than the pre-tax rate (impossible with a positive tax rate) and any option equal to the pre-tax rate multiplied by T alone.
• Link to WACC and capital structure theory. Be ready to explain that the tax deductibility of interest is the primary reason debt lowers WACC (Modigliani-Miller with taxes), and that the benefit is offset at high leverage by financial distress and agency costs.
• Manage your time. These are typically one-step or two-step calculations. Do them quickly and accurately, then move on; do not over-think a question that simply wants Kd × (1 − T).
7. Quick Practice Questions
Q1. A company's bonds yield 9%. Its marginal tax rate is 30%. What is the after-tax cost of debt?
Answer: 9% × 0.70 = 6.3%
Q2. A firm's after-tax cost of debt is 5.6% and its marginal tax rate is 20%. What is the pre-tax cost?
Answer: 5.6% / 0.80 = 7.0%
Q3. A firm has 30% debt at a pre-tax cost of 6%, 10% preferred stock costing 8%, and 60% common equity costing 11%. Tax rate 25%. What is WACC?
Answer: Debt after-tax = 6% × 0.75 = 4.5%. WACC = 0.30 × 4.5% + 0.10 × 8% + 0.60 × 11% = 1.35% + 0.80% + 6.60% = 8.75% (note preferred is not tax-adjusted).
Q4. Which of the following would increase a firm's after-tax cost of debt? (a) An increase in the corporate tax rate; (b) A decrease in the corporate tax rate; (c) A credit rating upgrade; (d) A decline in market interest rates.
Answer: (b). A lower tax rate shrinks the tax shield, raising the after-tax cost. Options (c) and (d) lower the pre-tax cost, and (a) lowers the after-tax cost.
Q5. A firm has substantial net operating loss carryforwards and expects to pay no income tax for several years. Its bonds yield 7%. What is its effective after-tax cost of debt?
Answer: 7%. With no taxable income, there is no current tax shield, so the after-tax cost equals the pre-tax cost.
8. Summary
The after-tax cost of debt measures what borrowing truly costs a company after accounting for the tax deductibility of interest. It is calculated as the pre-tax yield on new debt multiplied by (1 − marginal tax rate). It is always lower than the pre-tax cost for a tax-paying firm, it is the only component of WACC that receives a tax adjustment, and it rises when tax rates fall. For the CTP exam, master the formula, know when to use YTM versus coupon, remember to use the marginal tax rate, never tax-adjust equity or preferred stock, and sanity-check that your answer is below the pre-tax rate. With these habits, after-tax cost of debt questions become reliable points on exam day.
Test mode:
CTP - After-Tax Cost of Debt Example Questions
Test your knowledge of After-Tax Cost of Debt
Question 1
Why does a WACC calculation apply a tax adjustment to the component cost of debt while leaving the cost of equity unadjusted?
Question 2
A treasury analyst is updating the company's weighted average cost of capital (WACC). The company's outstanding bonds carry a 5% coupon but now trade at a yield to maturity of 6%. The company's marginal tax rate is 25%. Which cost of debt should the analyst enter in the WACC calculation (rounded to two decimals)?
Question 3
A company's outstanding bonds carry a 4% coupon and currently trade at a 6% yield to maturity. New debt of similar terms would price at that market yield. The statutory tax rate is 21%, but the company has large net operating loss carryforwards and expects no taxable income over the planning horizon. Which component cost of debt should the treasury analyst use in the WACC for a new project?
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