AGI Calculator
Calculate your Adjusted Gross Income (AGI) with common income sources and above-the-line deductions using a 2026 planning worksheet.
After-Tax Cost of Debt Calculator
Calculate the after-tax cost of debt including tax shield savings, effective interest rates, and lifetime interest analysis for corporate and personal debt.
Pre-Tax Cost of Debt⧉
0.06%
The nominal interest rate before considering tax benefits
After-Tax Cost of Debt⧉
0.05%
Reduced from 0.06% due to tax deductibility
Annual Interest Expense⧉
$30,000.00
Total interest paid per year before tax savings
Annual Tax Shield⧉
$6,300.00
Amount saved annually through interest deduction
Net After-Tax Interest⧉
$23,700.00
Actual annual cost after tax savings
Effective After-Tax Rate⧉
0.05%
Considers compounding frequency
All-In Cost Rate⧉
0.05%
Includes additional fees in cost calculation
Total Lifetime Savings⧉
$63,000.00
Over 10 years from tax deductions
Cost Comparison
Pre-Tax Cost0.06%
After-Tax Cost0.05%
| Year | Interest | Tax Shield | After-Tax Cost | Cum. Interest | Cum. Savings |
|---|---|---|---|---|---|
| 1 | $30,000.00 | $6,300.00 | $23,700.00 | $30,000.00 | $6,300.00 |
| 2 | $30,000.00 | $6,300.00 | $23,700.00 | $60,000.00 | $12,600.00 |
| 3 | $30,000.00 | $6,300.00 | $23,700.00 | $90,000.00 | $18,900.00 |
| 4 | $30,000.00 | $6,300.00 | $23,700.00 | $120,000.00 | $25,200.00 |
| 5 | $30,000.00 | $6,300.00 | $23,700.00 | $150,000.00 | $31,500.00 |
| 6 | $30,000.00 | $6,300.00 | $23,700.00 | $180,000.00 | $37,800.00 |
| 7 | $30,000.00 | $6,300.00 | $23,700.00 | $210,000.00 | $44,100.00 |
| 8 | $30,000.00 | $6,300.00 | $23,700.00 | $240,000.00 | $50,400.00 |
| 9 | $30,000.00 | $6,300.00 | $23,700.00 | $270,000.00 | $56,700.00 |
| 10 | $30,000.00 | $6,300.00 | $23,700.00 | $300,000.00 | $63,000.00 |
Planning notes, formulas, and examples
About the After-Tax Cost of Debt Calculator
The after-tax cost of debt represents the true cost of borrowing after accounting for the tax deductibility of interest payments. Because interest expenses can be deducted from taxable income, the effective cost of debt is lower than the stated interest rate. This concept is fundamental in corporate finance and is a key component in calculating the Weighted Average Cost of Capital (WACC).
Understanding your after-tax cost of debt helps make better capital structure decisions. Companies often prefer debt financing over equity precisely because of this tax advantage — known as the "tax shield." The tax shield effectively reduces the cost of borrowing by the company's marginal tax rate, making debt a more attractive financing option.
This calculator helps you determine the real cost of borrowing by factoring in your marginal tax rate, compounding frequency, and additional fees. Whether you're evaluating a corporate bond issuance, a business loan, or comparing financing options, knowing the after-tax cost gives you the true picture of what debt costs your organization.
When This Page Helps
Knowing the after-tax cost of debt is essential for any business evaluating financing options. It helps CFOs and financial analysts compare the true cost of debt versus equity financing, optimize capital structure, and accurately calculate WACC for investment decisions. It gives instant tax shield analysis and lifetime cost projections.
How to Use the Inputs
- Enter the total debt principal amount in dollars
- Input the annual interest rate charged on the debt
- Specify your marginal tax rate (corporate or personal)
- Set the loan term in years for lifetime analysis
- Choose the compounding frequency (annual, quarterly, monthly)
- Add any additional annual fees or costs
- Review the after-tax cost and tax shield savings
Formula used
After-Tax Cost of Debt = Interest Rate × (1 − Tax Rate)
Where:
- Interest Rate = annual nominal interest rate (as decimal)
- Tax Rate = marginal tax rate (as decimal)
- Tax Shield = Annual Interest × Tax Rate
- Effective Rate = (1 + r/n)^n − 1 for n compounding periodsExample Calculation
Result: 4.74% after-tax cost
A $500,000 loan at 6% interest with a 21% tax rate yields an after-tax cost of 4.74%. The annual tax shield is $6,300 ($30,000 interest × 21%), saving $63,000 over the 10-year term.
Tips & Best Practices
- Use the marginal (not effective) tax rate for the most accurate result
- Include all fees in the additional costs field for a true all-in cost
- Compare after-tax costs across different loan offers to find the cheapest financing
- Remember that tax shields only apply if the company is profitable and paying taxes
- Consider the after-tax cost when deciding between debt and equity financing
Why The Tax Shield Matters
The headline interest rate on a loan is not always the economic cost of borrowing. If the interest expense is deductible, part of that cash outflow is offset by lower taxes. That is why the after-tax cost of debt matters in WACC work, project finance, and capital-structure comparisons.
When The Formula Breaks Down
The simple `interest rate × (1 - tax rate)` shortcut assumes the borrower can actually use the deduction and that the tax shield is not limited. Real-world limits can arise from low taxable income, interest limitation rules, entity structure, or personal-interest rules that make some borrowing nondeductible.
Use It For Scenario Planning
This page is most useful when you compare financing options under the same tax assumptions. Test a conservative marginal tax rate, include annual fees, and compare the after-tax cost against your hurdle rate or return on invested capital before treating debt as automatically cheaper than equity.
Sources & Methodology
Last updated:
Methodology
This worksheet applies the standard shortcut after-tax cost of debt = interest rate × (1 − marginal tax rate), then layers on annual-interest, tax-shield, effective-rate, and fee illustrations using the user-entered principal, compounding frequency, term, and annual fees. It is best read as a planning worksheet for comparing debt scenarios under a chosen marginal tax assumption rather than as a full tax-return model.
The output does not prove that every dollar of interest is deductible. Real deductibility can be limited by entity type, taxable-income position, personal-use rules, or business-interest limitation rules under section 163(j), so the tax shield shown here should be confirmed against the borrower's actual tax posture.
Sources
- About Form 8990, Limitation on Business Interest Expense Under Section 163(j) (Internal Revenue Service) — IRS reference for current-law business-interest deduction limits that can reduce the assumed tax shield.
- Guide to business expense resources (Internal Revenue Service) — IRS resource hub for business-interest and deductible-expense guidance used when framing after-tax borrowing cost.
Frequently Asked Questions
It is the effective interest rate a company pays on its debt after accounting for income tax deductions on interest payments. Since interest is tax-deductible, the real cost is lower than the nominal rate.
It is a key input in WACC and helps companies compare debt financing with equity financing on a comparable after-tax basis. The bigger the tax shield, the lower the effective borrowing cost.
Interest payments reduce taxable income. If a company pays $100,000 in interest and has a 25% tax rate, it saves $25,000 in taxes, effectively reducing the cost of that interest.
Use the marginal tax rate that actually applies to the interest deduction you are modeling. For U.S. corporate debt, the federal corporate rate is still 21% under current law, but state taxes, limitation rules, and entity structure can change the real tax shield.
Yes. More frequent compounding increases the effective interest rate and thus the effective after-tax cost, though the difference is typically small.
The cost approaches zero only if the tax rate is near 100%, which is unrealistic. In practice, after-tax cost is always positive but significantly lower than the pre-tax rate.
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