Get the definition right first. The cost of debt is the rate at which the company could borrow long-term, today, in the valuation currency. It's the marginal rate. Coupons on bonds issued in 2021 don't qualify. Neither does interest expense ÷ book debt, which is the embedded historical average and useful as a cross-check, nothing more. Lenders reprice a company every day whether or not it borrows, and your job is to read today's price. There are three routes, in order of preference:
Route 1: traded bonds. If the company has a liquid, straight (no embedded options), long-dated bond outstanding, its yield to maturity is the market's answer, directly. In the US you get bond prices and yields free from FINRA's TRACE data. India's corporate bond market is thin. NSE/BSE debt segments list trades, but liquid long benchmark bonds exist mainly for the largest issuers (REC, PFC, HDFC-family, the AAA PSUs). Use this route when you can. Usually you can't.
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How do you use a credit rating to find the cost of debt?
Route 2: the rating, if one exists. Take the issuer's senior rating and add the current spread for that rating to the risk-free rate: Rd = Rf + default spread(rating). US ratings come from Moody's/S&P/Fitch and are disclosed in filings and press releases. India has a trap here. CRISIL/ICRA/CARE ratings are national-scale. "CRISIL AAA" means safest relative to other Indian issuers, and it isn't a global AAA. Because of the sovereign ceiling, the same issuer would map to around the sovereign's Baa3/BBB on a global scale. Never pull a global spread table with a national-scale rating. There's a workable Indian shortcut, though. A domestic-AAA blue chip borrows near G-sec + 30–80bp in INR, and you can see it in its actual fresh borrowings in the annual report's borrowing note.
How does a synthetic rating work for unrated firms?
Route 3: the synthetic rating. Most analysts lack this skill. Most companies worldwide, and most Indian companies, have no traded bonds and no meaningful rating. Damodaran's fix rests on one observation: ratings are largely reverse-engineerable from one ratio. Agencies weigh many factors, but interest coverage does most of the work:
Interest coverage ratio (ICR) = EBIT ÷ interest expenseMap the ICR to a rating, and the rating to a current market spread, using his lookup table at Damodaran Online → Current Data → "Ratings, Interest Coverage Ratios and Default Spread". That's the ratings.xls sheet, with spreads refreshed each January from traded-bond data. Thresholds are stable across years, but spreads move. Treat the numbers below as an early-2026-vintage illustration, and always pull the live sheet. Here's the table's shape for large non-financial firms (market cap > $5bn):
| ICR (large caps) | Synthetic rating | Illustrative spread |
|---|---|---|
| > 8.5 | Aaa/AAA | ~0.6% |
| 6.5 – 8.5 | Aa2/AA | ~0.7% |
| 5.5 – 6.5 | A1/A+ | ~0.8% |
| 4.25 – 5.5 | A2/A | ~1.0% |
| 3.0 – 4.25 | A3/A− | ~1.2% |
| 2.5 – 3.0 | Baa2/BBB | ~1.6% |
| 2.25 – 2.5 | Ba1/BB+ | ~2.0% |
| 2.0 – 2.25 | Ba2/BB | ~2.4% |
| 1.75 – 2.0 | B1/B+ | ~3.0% |
| 1.5 – 1.75 | B2/B | ~3.7% |
| 1.25 – 1.5 | B3/B− | ~4.5% |
| 0.8 – 1.25 | Caa/CCC | ~8% |
| 0.65 – 0.8 | Ca2/CC | ~10% |
| 0.2 – 0.65 | C2/C | ~13% |
| < 0.2 | D2/D | ~16%+ |
A parallel table for smaller firms (< $5bn market cap) demands roughly 1.5× the coverage for the same rating. AAA needs ICR > 12.5, for example. An ICR of 4 lands around Ba1/BB+. Small firms are riskier at the same coverage, and most Indian mid-caps use this table. You'll find both tables in the same sheet.
How do you assemble and cross-check the pre-tax rate?
Now assemble the rate, with the emerging-market layer where it applies. For a US firm, Rd = Rf(USD) + company spread. For an Indian firm borrowing in rupees, the sovereign's own default risk comes between the clean risk-free rate and any company's borrowing cost:
Rd(INR) = Rf(clean INR) + country default spread + company spread
= 4.5% + 2.0% + company spread (illustrative)Cross-check against reality every time. Look at the borrowing note in the annual report, which discloses actual recent borrowing rates. Then interest expense ÷ average gross debt gives you the embedded average. Your synthetic estimate should be in their neighborhood, and for fresh borrowing it should be nearer the marginal disclosures. Once in a while a giant with fortress cash flows and mostly-offshore revenue can borrow below its sovereign. If the disclosed rates say so, believe the disclosures.
How do you take it after tax, and when does it break down?
Then take it after tax, at the marginal rate. Interest is tax-deductible, so debt's true cost is Rd × (1 − t). Here t is the marginal statutory rate, the rate on the next rupee of pre-tax income, because that's what the shield saves. Don't use the effective rate. It's an average polluted by one-offs, credits, and geography, as the ETR reconciliation from your work on liabilities and financing showed. For India use ≈ 25.17%, which is the 22% new-regime rate plus surcharge and cess. Older-regime firms pay ~34.9%. Check the tax note. Our drills round India to 25%. For the US use ≈ 25% (21% federal + typical state).
One brutal caveat. The shield exists only if there's income to shield, so a loss-making firm's after-tax cost of debt is its pre-tax cost until profits, and tax payments, return.
There's a distress caveat too, about expected versus promised yields. A bond yielding 19% because default looms doesn't give the firm a 19% expected cost of debt. That YTM is a promised rate on money the lenders doubt they'll see. For healthy firms the distinction is negligible. For distressed ones, cap the synthetic-rating spread logic with judgment and lean on the distressed toolkit in the special-situations capstone. Flag it, and don't fake precision.