Debt Capacity and Coverage-Based Debt Sizing

Ask a company how much debt it wants and the honest answer is often "as much as possible" — debt is usually cheaper than equity and doesn't dilute ownership. Lenders don't work off that number. They size debt around a much more grounded question: given the company's cash flow, how big a loan can it service and still have a cushion if things go a little wrong? That question, formalized, is debt capacity, and lenders typically get there through coverage-based sizing rather than simply capping the total amount borrowed.

The core ratio

$$\text{Interest coverage} = \frac{\text{EBITDA}}{\text{Interest expense}}$$

In words: EBITDA — earnings before interest, tax, depreciation and amortization, used as a rough proxy for operating cash flow — divided by the interest the company must pay. A ratio of 3x means the company generates three dollars of operating cash flow for every dollar of interest owed; a ratio near 1x means almost all operating cash flow is consumed just servicing interest, leaving no margin for a bad quarter.

Lenders typically work backward from a minimum acceptable coverage ratio to find the maximum debt they're willing to extend:

$$\text{Max debt} = \frac{\text{EBITDA}}{\text{minimum coverage} \times \text{interest rate}}$$

In words: take the company's EBITDA, decide the smallest coverage cushion you're willing to accept, and back into the loan size that interest rate and cushion imply.

Worked example

A company generates $50 million of EBITDA. A lender wants at least 3x interest coverage before extending a loan, and the loan would carry a 7% interest rate.

1. Maximum interest the lender will let the company pay. $50 / 3 = 16.67$, i.e. $16.67m of interest per year is the most the lender wants the company obligated to pay.
2. Maximum loan size. $16.67 / 7\% = 238$, i.e. $238m. That is the debt capacity implied by a 3x coverage requirement at a 7% rate.

If the company already has $100 million of existing debt at that same rate, its remaining debt capacity under this test is roughly $238 - 100 = 138$, i.e. $138m — that's the ceiling on new borrowing before coverage falls below the lender's floor.

What this means in practice

Leveraged finance desks, private equity sponsors sizing an LBO, and rating agencies all lean on coverage-based sizing as their primary discipline, often alongside a total-leverage test (debt / EBITDA) as a second check. Coverage ratios matter more in rising-rate environments, because the same debt load requires more interest coverage as rates climb — a company that comfortably covered its debt at 4% rates can breach covenants at 8% rates with no change in its EBITDA at all.