Cheap debt can make almost any financing strategy look smart.
When interest rates are low, companies can borrow inexpensively, refinance old obligations, fund acquisitions, and sometimes repurchase shares without dramatically increasing interest expense.
But the same capital structure can become uncomfortable when rates rise and yesterday’s low-cost debt starts maturing.
That is why optimising capital structure across different interest rate environments requires more than choosing between debt and equity once and forgetting about it.
Capital structure is the combination of debt, equity, and sometimes hybrid financing a company uses to fund its assets and operations.
CFA Institute describes one major objective as finding a financing mix that can reduce the weighted-average cost of capital, or WACC, while considering taxes, financial distress, and other real-world constraints.
The smartest structure is rarely the one with the cheapest financing today.
It is the one that remains manageable when interest rates, credit spreads, cash flow, and refinancing conditions change tomorrow.
Start With WACC, but Do Not Optimise It in Isolation
The weighted-average cost of capital combines the required returns of debt and equity according to how much each source contributes to company financing.
Debt is often cheaper than equity, partly because lenders generally take less risk than shareholders and interest expenses may receive favorable tax treatment depending on local tax rules.
That can make adding debt look attractive.
Imagine a company financed entirely with equity where shareholders require a 10% return. If it can replace some equity financing with debt costing 5%, its overall financing cost may initially fall.
But leverage cannot increase forever.
As borrowing rises, lenders may demand higher interest rates because default risk increases. Shareholders can also demand higher expected returns because equity becomes riskier.
Eventually, the apparent advantage of cheap debt can disappear.
CFA Institute therefore emphasizes that optimal capital structure involves balancing potential benefits of debt against financial-distress costs rather than simply maximizing leverage.
Low-Rate Environments Can Encourage More Debt
When policy rates and bond yields are low, companies often have an opportunity to lock in relatively inexpensive financing.
This can be particularly attractive for companies with predictable cash flows.
Imagine a business planning a $500 million expansion expected to generate stable returns for 15 years. If it can issue long-term fixed-rate debt at 3%, management may prefer borrowing rather than issuing a large amount of new equity and diluting existing shareholders.
Low-rate periods can also be useful for refinancing.
A company carrying older debt at 7% might replace it with new bonds costing 4%, immediately reducing future interest expenses.
But there is a trap.
Cheap money can encourage businesses to borrow more simply because borrowing looks inexpensive.
IMF research has found evidence that lower interest rates can encourage greater risk-taking in credit markets.
A company should therefore ask whether debt is financing productive assets – or merely expanding leverage because financing is easy.
The best time to build financial flexibilty is often when capital is still cheap.
Rising Rates Make Debt Structure More Important
Interest-rate increases do not affect every company at the same speed.
A company with mostly long-term fixed-rate bonds may feel surprisingly little immediate pressure.
A business funded with floating-rate loans can feel the change much faster.
Federal Reserve research notes that bank loans are predominantly floating-rate obligations, meaning their servicing costs can respond relatively directly to increases in policy rates. Fixed-rate corporate bonds can delay that pass-through until refinancing occurs.
Consider two companies, each with $1 billion of debt.
Company A has locked most of its borrowings at 4% for another eight years.
Company B relies heavily on floating-rate loans that move from 4% to 7%.
Company B’s annual interest cost could rise dramatically even though both firms technically have the same amount of debt.
This is why capital-structure analysis should examine rate exposure, not simply total leverage.
Balance Fixed-Rate and Floating-Rate Borrowing
Fixed-rate debt offers predictability.
Management knows approximately what interest payments will look like even if market rates rise sharply.
The disadvantage appears when rates fall.
A company locked into expensive fixed-rate borrowing may continue paying above-market interest unless it can refinance economically.
Floating-rate debt behaves in the opposite way.
It may become cheaper when central banks cut rates, but borrowing costs can rise quickly during tightening cycles.
The ideal combination depends on cash-flow stability, industry conditions, debt maturity, hedging capacity, and management’s willingness to tolerate interest-rate volatility.
A highly cyclical company may prefer more predictable fixed-rate financing because its earnings could weaken at exactly the same time interest rates or credit spreads become difficult.
A company with substantial cash and stable recurring revenue may tolerate greater floating-rate exposure.
There is no universal fixed-versus-floating ratio.
The objective is avoiding a situation where one rate scenario can destabilise the entire balance sheet.
Build a Maturity Ladder to Reduce Refinancing Risk
Interest cost is only one part of debt management.
Maturity timing can be just as important.
Suppose a company has $3 billion of bonds and all of them mature in 2028.
That creates a concentrated refinancing event.
If credit markets are healthy in 2028, the company may refinance easily.
But what if the maturity arrives during a recession, banking crisis, or period of extremely high interest rates?
The company could be forced to refinance at unattractive rates – or struggle to raise money at all.
A maturity ladder spreads obligations across several years.
Instead of refinancing $3 billion at once, the company might have $500 million maturing in each of several different periods.
Federal Reserve research has found that companies with more debt approaching maturity can be more sensitive to monetary-policy changes because their refinancing needs expose them more directly to prevailing real interest rates.
BIS research similarly found that firms used low-rate periods to extend debt maturities and issue fixed-rate borrowing, while later increases in rates created greater rollover pressure as that debt approached maturity.
Good capital structure therefore manages when financing must be renewed, not merely how much it costs today.
High-Rate Environments Reward Strong Liquidity
When borrowing becomes expensive, cash suddenly becomes more valuable.
A company with substantial liquidity can delay refinancing, fund investment internally, or wait until market conditions improve.
A highly leveraged company with little cash has fewer choices.
Federal Reserve research on corporate debt-servicing capacity specifically uses interest coverage – the ratio of EBIT to interest expense – to evaluate whether companies generate enough operating earnings to handle borrowing costs.
Suppose a company produces $300 million of EBIT and pays $50 million of annual interest.
Its interest coverage ratio is 6 times.
If refinancing pushes interest expense to $100 million while earnings remain unchanged, coverage falls to 3 times.
Now imagine a recession simultaneously reduces EBIT to $220 million.
Coverage falls again to 2.2 times.
This illustrates why analysing debt under a single interest-rate assumption is dangerous.
Management should stress-test both financing costs and operating earnings.
Refinancing Risk Can Arrive With a Delay
One of the confusing things about rising interest rates is that their corporate impact can take years to appear.
A company may report healthy profits even after market rates have risen dramatically because its existing debt was issued earlier at low fixed rates.
The real pressure emerges when those bonds mature.
The Federal Reserve noted in its April 2025 Financial Stability Report that higher rates had passed through only gradually to many public companies because a large share of liabilities was long-term and fixed-rate.
It also warned that refinancing needs could increase the transmission of higher borrowing costs over subsequent years.
The BIS has highlighted a similar risk: companies refinancing maturing debt can face substantially higher costs when benchmark rates and credit spreads are above the levels prevailing when the debt was originally issued.
Management should therefore monitor future refinacing schedules before the problem reaches the income statement.
Waiting until maturity is six months away can leave very few options.
Falling Rates Create Refinancing Opportunities
A declining-rate environment changes the equation again.
Companies carrying expensive debt may have opportunities to refinance at lower rates, subject to call provisions, transaction costs, and credit-market conditions.
Suppose a company has $800 million of bonds paying 7%.
If comparable new debt becomes available near 5%, replacing the old financing could eventually save roughly $16 million annually before fees and other considerations.
Falling rates can also change the relative attractiveness of debt-funded acquisitions or capital investment.
But management should not automatically increase borrowing simply because rates are falling.
Credit spreads may remain elevated during recessions, meaning government yields could decline while corporate financing remains expensive.
A central-bank rate cut also does not guarantee that every company receives cheaper credit.
Companies with deteriorating earnings may actually face higher spreads because lenders are becoming more concerned about default.
Always separate risk-free rates from company-specific credit costs.
Use Equity When Balance-Sheet Resilience Matters More Than Dilution
Issuing equity can feel expensive because existing shareholders give up part of their ownership.
But equity has one major advantage over traditional debt:
There is generally no contractual interest payment or maturity date.
That can be extremely valuable when leverage is already high.
Suppose a company needs $500 million for expansion but its debt ratio is elevated and several bonds mature within three years.
Adding another $500 million of debt may look cheaper on a spreadsheet.
However, an equity issue could strengthen the balance sheet, preserve borrowing capacity, and reduce the probability that a future downturn creates financial distress.
The best decision therefore depends on marginal financing risk, not just today’s headline cost.
Capital structure should preserve room to respond to future opportunities and shocks.
A company that uses every dollar of borrowing capacity during good times may discover it has none available when an exceptional acquisition or unexpected crisis arrives.
Stress-Test the Capital Structure Across Several Rate Scenarios
The most practical way to evaluate financing resilience is scenario analysis.
Do not forecast one interest-rate path.
Test several.
Start with the current borrowing cost. Then model rates 100, 200, or 300 basis points higher when major debt matures.
Add another scenario where earnings decline 20% during the same period.
Then examine interest coverage, free cash flow, leverage, covenant headroom, liquidity, and refinancing requirements.
Federal Reserve scenario analysis found that the aggregate U.S. public corporate sector could tolerate sustained elevated rates reasonably well under some conditions, but firms with weaker balance sheets became considerably more vulnerable when higher rates were combined with declining earnings.
That interaction is the real danger.
Companies rarely fail simply because interest rates rise.
Problems become serious when expensive refinancing, weaker profits, reduced liquidity, and tighter lending conditions arrive together.
Capital Structure Should Change With the Business
An “optimal” capital structure is not permanent.
A young technology company with uncertain cash flow may sensibly use very little debt.
Ten years later, the same company could have recurring revenue, large cash reserves, and predictable earnings that support moderate leverage.
A utility with stable cash flows may tolerate considerably more debt than a cyclical commodity producer.
Acquisitions, asset sales, recessions, tax changes, credit-rating objectives, and shifts in interest rates can all change the appropriate financing mix.
CFA Institute emphasizes that estimating WACC requires assumptions about a company’s target capital structure, which may differ from the financing mix currently shown on the balance sheet.
That is an important distinction.
Management should not defend yesterday’s debt-equity ratio simply because it already exists.
Capital allocation should evolve with the company’s cash flows and financing enviroment.
Optimising capital structure is not about finding the maximum amount of debt a company can borrow or always choosing the cheapest financing available today.
The stronger approach balances debt costs, equity dilution, interest-rate exposure, maturity timing, liquidity, refinancing risk, and financial flexibility.
Low-rate environments can offer opportunities to lock in long-term financing. Rising rates make fixed-versus-floating exposure increasingly important, while high-rate periods reward liquidity and disciplined maturity management.
Falling rates can create refinancing opportunities but should not automatically trigger additional leverage. Review the capital structure under several interest-rate and earnings scenarios rather than one forecast.
If the balance sheet remains workable when borrowing costs rise and profits weaken, the company has something more valuable than cheap financing: room to make decisions when conditions become difficult.
