How to Calculate Cost of Debt — Step-by-Step with Real Data (India)
Core Claim: Debt looks cheap, but it creates value only when companies earn returns higher than its true (after-tax) cost.
Series Context (Don't Break the Chain)
This article is part of the Financial Modelling & Valuation Series.
In the previous article (Step 5): How to Calculate Cost of Equity, we calculated the required return for shareholders.
Now: We calculate Cost of Debt and correctly treat Preference Shares before moving to WACC.
Why Cost of Debt Matters
- Tax shield reduces effective cost
- Fixed obligations increase downside risk
- Leverage amplifies outcomes
The Formula (After-Tax Cost of Debt)
Cost of Debt = Interest Rate × (1 − Tax Rate)
Step 1: Effective Interest Rate (Use Actuals)
Interest Rate = Interest Expense / Average Total Debt
- Example: ₹500 Cr / ₹5,000 Cr = 10%
Step 2: Tax Shield
- Corporate tax (India) ≈ 25%
After-Tax CoD = 10% × (1 − 0.25) = 7.5%
RBI Monetary Policy → Cost of Debt (Transmission)
- Repo ↑ → MCLR/Eff. lending rates ↑ → CoD ↑
- Repo ↓ → Borrowing cost ↓ → CoD ↓
Interest Rate Risk: Floating-rate loans reprice quickly; fixed-rate loans reprice at refinancing. Both paths increase CoD in tightening cycles.
Preference Shares — Correct Treatment (Critical)
Preference shares sit between debt and equity. Misclassification distorts WACC.
| Feature | Debt | Preference Shares | Equity |
|---|---|---|---|
| Fixed payment | Yes (Interest) | Yes (Dividend) | No |
| Tax deductibility | Yes | No | No |
| Priority | Highest | Above Equity | Lowest |
| Maturity | Fixed | Often perpetual/long-dated | Perpetual |
Cost of Preference Shares
Cost of Preference = Preference Dividend / Net Proceeds (Market Value)
Where to Place in WACC?
- Include as a separate component (preferred)
- Or club with equity if small/immaterial
When Analysts Misclassify (Common Error)
- Including preference in debt → Understates WACC
- Ignoring preference entirely → Overstates equity returns
Real Insight (Cyclical Businesses)
- Cash flows volatile; obligations fixed
- Leverage magnifies peak and pain
Comparison — Cost of Debt (India)
| Company | Sector | Interest Rate | After-Tax CoD | Risk |
|---|---|---|---|---|
| Tata Steel | Steel | 9.5% | 7.1% | High |
| JSW Infra | Infra | 10.5% | 7.9% | High |
| UltraTech Cement | Cement | 8.5% | 6.4% | Moderate |
| ONGC | Oil & Gas | 7.5% | 5.6% | Low |
Top Searched Questions — Integrated
What is a good cost of debt in India? → ~6%–9% (after tax), varies by credit quality and cycle.
Why is cost of debt lower than equity? → Senior claim + contractual payments → lower required return.
How do RBI rate hikes affect CoD? → Immediate increase for floating debt; lagged increase via refinancing for fixed debt.
Does inflation impact CoD? → Yes, higher inflation → higher policy rates → higher CoD.
Fixed vs floating — which is riskier? → Floating carries rate risk; fixed carries refinancing risk.
How to compute real CoD from statements? → Interest expense / average debt; adjust for one-offs.
Should I use book or market debt? → Use market-consistent cost; weights in WACC should be market values.
Can CoD change without new borrowing? → Yes, via rate resets and covenant step-ups.
Are preference shares part of debt? → No for CoD; treat separately (no tax shield).
How to calculate cost of preference shares? → Dividend / market value; no (1−T) adjustment.
Common Mistakes
- Ignoring tax shield
- Using outdated/teaser rates
- Ignoring floating-rate exposure
- Misclassifying preference shares
- Not modeling refinancing risk
Golden Rule
What Comes Next
Combine Cost of Equity + Cost of Debt + Preference Cost into:
WACC — The True Cost of Capital
Final Conclusion
Cost of Debt reflects rates, credit risk, and policy. Preference shares add fixed cost without tax shield. Model both correctly to avoid understating WACC.
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