The Cost of Debt Formula: How to Calculate and What It Means for Your Business

Navigating the financial landscape is a paramount task for small business owners, and a significant part of that journey is understanding the cost of debt. This seemingly simple term holds profound implications for a business's financial health and its ability to thrive in competitive markets.

Cost of debt, essentially the interest expense, is the price tag attached to the borrowed capital, reflecting the cost of maintaining outstanding debts. With a ripple effect on a company’s bottom line, mastering the cost of debt is not just about number-crunching but a stride towards achieving financial robustness and long-term sustainability. 

In the ensuing sections, we’ll delve deeper into unraveling the cost of debt, its calculation, and its bearing on making informed financial decisions.

Understanding Cost of Debt

Cost of debt is essentially the interest expense incurred by a business, representing the total interest paid on all loans. This financial metric is pivotal as it influences your company’s bottom line. The lower your interest rates, the lower your cost of debt – an ideal scenario for any business. 

Credit scores play a crucial role in determining your interest rates. Lenders delve into your financial health, scrutinizing documents like balance sheets to ascertain your creditworthiness. A favorable credit rating can significantly lower your interest rates, ultimately reducing your cost of debt. Hence, working towards improving your credit score is a strategic move to optimize your business finances and achieve a lower cost of debt.

Calculating Cost of Debt

Understanding the cost of your debt is pivotal for managing your business finances efficiently. 

There are two primary ways to calculate the cost of debt: one is the pre-tax cost of debt, and the other is the after-tax cost of debt.

Pre-tax Cost of Debt

The formula to determine the pre-tax cost of debt is straightforward:

Total Interest / Total Debt = Cost of Debt

First, you’ll need to find your total interest by multiplying each loan by its respective interest rate, then summing those numbers together. 

Next, calculate your total debt by adding up all your loans. 

Finally, divide the total interest by the total debt to ascertain your cost of debt.

After-tax Cost of Debt

For the after-tax cost of debt, the formula slightly adjusts to account for tax deductions on interest expenses:

Effective Interest Rate x (1 – Effective Tax Rate) 

The effective interest rate is the weighted average interest rate derived from the pre-tax cost of debt calculation. You’ll need to know your tax rate to complete this calculation. 

Firstly, subtract your effective tax rate from one. 

Then, multiply the resulting figure by your effective interest rate to get your after-tax cost of debt.

Both calculations are crucial to understand the financial health of your business and to make informed financial decisions moving forward.

Practical Example

Navigating through financial metrics can often seem like maneuvering through a dense fog. However, with a clear example, the haze will start to lift. Let’s journey through a real-world scenario to shed light on how to calculate the cost of debt manually.

Suppose your burgeoning enterprise has secured three loans:

  • Small Business Loan: $50,000 at a 5% annual interest rate.
  • Business Credit Card: $10,000 at a 20% annual interest rate.
  • Line of Credit: $5,000 at a 15% annual interest rate.

Pre-tax Cost of Debt

The formula to navigate here is: Total Interest / Total Debt = Cost of Debt

To find our total interest, we’ll multiply each loan amount by its respective interest rate, then sum up the results:

  • $50,000 x 0.05 = $2,500
  • $10,000 x 0.20 = $2,000
  • $5,000 x 0.15 = $750

Summing these up gives us a total interest of $5,250.

Next, we’ll sum up all our loans to get the total debt: $50,000 + $10,000 + $5,000 = $65,000

Now, applying the formula: $5,250 / $65,000 = 0.08 or 8%. 

This is our pre-tax cost of debt.

After-tax Cost of Debt

Now, for the after-tax cost of debt, the formula morphs into: Effective Interest Rate x (1 – Effective Tax Rate)

Let’s say our effective tax rate is 25%. The calculation then becomes: 8% x (1 – 0.25) = 6%

With this simple yet illustrative example, you now have a torch to guide you through the foggy terrain of calculating your business’s cost of debt. 

So, the next time financial clouds loom, you’ll have the formula to find your way.

Comparison with Other Financial Metrics

Understanding your cost of debt is pivotal, but it’s merely one piece of the financial puzzle. Comparing it to other vital metrics like the cost of equity and the Weighted Average Cost of Capital (WACC) can provide a more holistic view of your business’s financial health. The cost of equity represents the return required by an equity investor to hold shares of your business, contrasting the interest expense in cost of debt. 

WACC, on the other hand, provides a broader perspective by blending the cost of debt and equity, offering insight into the average cost per dollar of financing. Through these comparisons, you gain a clearer understanding of your financial standing, enabling more informed decision-making.

Impact on Decision-Making

Understanding the cost of debt is pivotal for astute financial decision-making. It’s more than just a number; it’s a reflection of your business’s financial health. By evaluating your cost of debt, you can better strategize on loan management and negotiate favorable terms with lenders. 

Moreover, a lower cost of debt enhances your company’s appeal to investors, showcasing prudent financial stewardship. It also frees up capital, allowing for reinvestment into growth-centric initiatives. Thus, mastering the cost of debt formula is not merely about crunching numbers—it’s about forging a robust path toward sustainable financial management and fostering a conducive environment for business growth.


Mastering the art of managing your business’s finances is crucial for sustained growth and stability. Understanding and controlling your cost of debt is a fundamental aspect of this mastery. By leveraging the formulas and strategies discussed, you can optimize your interest expenses, make informed borrowing decisions, and enhance your business’s financial health. 

Incorporating interactive tools and comparing various financial metrics will not only broaden your financial insight but also pave the way for strategic financial planning. As you stride forward in your entrepreneurial journey, let the mastery of cost of debt be the compass guiding your financial decisions.



Business Funds Marketplace is a financial services provider focused on helping to solve the cash flow needs of small businesses. The founders of Business Funds Marketplace are experienced financial service professionals who have significant experience in developing successful businesses. We treat you with the utmost respect and confidentiality, as a partner.

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