Cost of Debt Using Yield to Maturity: Formula & Example

You need to figure out exactly how much your borrowed capital is costing you. Or, you bought a bond and want to know your real return.

If you just look at the interest rate on the document, you will get the wrong answer. Market prices change, fees eat into returns, and taxes alter everything. You need to calculate the actual yield.

Here is the unvarnished math on calculating the cost of debt using yield to maturity.

What is the Yield on Debt?

The yield on debt is the effective return generated by a debt instrument. It is different from the stated interest rate (coupon rate).

When a company or a commercial real estate debt fund issues bonds, those bonds trade on the open market. The price goes up and down. Because the price moves but the interest payment stays the same, the yield changes constantly.

To run a basic yield on debt calculation, use the simple yield on debt formula:

Yield = Annual Interest Payment ÷ Current Market Price

If you want to know how to calculate yield on debt for a quick snapshot, this formula works. But it ignores the final principal repayment.

Understanding Yield to Maturity (YTM)

If you hold a bond until it ends, you need to calculate the yield to maturity.

The calculate yield to maturity of debt process accounts for three things: the interest payments, the price you paid, and the time left until the debt matures. It is the most accurate way of calculating market yield on debt.

When lenders quote a rate, they are often quoting the calculating promised yield on debt. This assumes the borrower makes every payment perfectly on time without defaulting.

If you want to know how to calculate yield to maturity of debt, the exact math requires trial and error or a financial calculator. You can use a standard cost of debt yield to maturity calculator to find it instantly.

Pretax vs. After-Tax Cost of Debt

Where interest is deductible and the deduction is usable, it can reduce the after-tax cost. Deductibility and limitations depend on the taxpayer and applicable rules.

First, you calculate pretax yield of debt (or calculate pre tax yield of debt). This is simply the YTM.

Next, you calculate the after-tax cost.

After-Tax Cost of Debt = Pretax Yield × (1 - Tax Rate)

If you are calculating cost of debt using yield to maturity, and your YTM is 8% with a 25% tax rate, your after-tax cost is 6%. If you search for a tool to calculate after tax cost of debt yield to maturity, it uses this exact formula.

Whether you are figuring out how to calculate cost of debt using yield to maturity or how to calculate yield on debt instrument, model taxes only under supported assumptions about the deduction and its timing.

After-Tax Cost of Debt for Irredeemable Debentures

For irredeemable (perpetual) debentures or bonds with no fixed maturity date, you do not need complex trial-and-error discounting because there is no principal balloon payment to discount. The formula divides annual coupon interest by the current net market price and applies the tax shield:

Kd = [Annual Interest × (1 - Tax Rate)] ÷ Current Market Price

Where:

• Annual Interest = Coupon payment per year
• Tax Rate = Corporate marginal tax rate
• Current Market Price = Market value or net proceeds (after issuance costs)

For example, if an irredeemable debenture with a $1,000 par value pays an 8% coupon ($80/year), trades in the market at $950, and the company pays a 25% tax rate:

Kd = [$80 × (1 - 0.25)] ÷ $950 = $60 ÷ $950 = 6.32%

When to Use YTM of Comparable Bonds

When a borrower, developer, or private CRE sponsor does not have publicly traded bonds with observable market prices, you cannot compute an empirical YTM directly from trading history. In corporate and institutional underwriting, you use the YTM of comparable bonds when:

1. The company is unrated or privately held: You find public corporate or REIT bonds with identical credit ratings, leverage profiles, and terms to maturity, and use their market YTM as your pre-tax cost of debt.
2. Pricing new construction or bridge debt: You benchmark against current secondary-market spreads of similar debt funds or CMBS tranches rather than relying on stale historical borrowing rates.
3. Calculating WACC for investment decisions: Stated interest on legacy loans reflects historical rates; the current market YTM of comparable debt reflects the true opportunity cost of capital today.

Frequently asked questions

What does yield on debt mean? Yield on debt is the annual return a lender earns on money it has loaned, expressed as a percentage of the amount at risk. For a bond it is the yield to maturity; for a commercial real estate loan the lender's own "debt yield" metric is NOI divided by loan amount. CRE debt yield is not a contractual investment return and should not be substituted for yield to maturity.

What is the formula for yield on debt? The simplest form is annual interest income divided by the debt's price or principal. For yield to maturity you solve for the discount rate that sets the present value of every future coupon and the final principal equal to today's price, which requires a financial calculator or trial and error. For a borrower's after-tax cost, multiply the pre-tax yield by (1 − tax rate).

How do you calculate the after-tax cost of debt from yield to maturity? Take the yield to maturity as the pre-tax cost, then apply the tax shield: After-Tax Cost of Debt = YTM × (1 − Tax Rate). At an 8% YTM and a 25% tax rate, the after-tax cost is 6%. Interest is tax-deductible, so debt is cheaper for a business than the headline rate suggests.

Is yield on debt the same as the interest rate? No. The interest rate is fixed by the loan contract. The yield reflects what the lender actually earns given the price paid and any upfront points or fees, so a 6% loan with 2 points upfront can carry an effective yield closer to 7.5%. The stated rate is the starting point; the yield is the truth.