CDS Index

Also known as: CDX, iTraxx

Default protection on 100+ names in one trade — the S&P 500 of credit risk.

3 min read · 613 words · Updated

1 · SnapshotThe one idea to remember
Key intuition: single-name CDS is a stethoscope on one company; the index is the thermometer for the whole market.
2 · BeginnerWhat is it, really?

A credit default swap is insurance against one company failing to pay its debts. A CDS index packs a long list of those into a single contract. The two main ones cover 125 solid companies each: CDX.IG in North America and iTraxx Europe. The riskier versions cover 100 shakier borrowers.

One trade insures the whole list at once — or sells that insurance to somebody else. The price of the index is the market's temperature reading on credit. Around 50 basis points a year means calm. Around 150 means worried. In the worst of 2008 the risky index reached 800, which is a market that expects a lot of companies to fail.

Trading the index is far cheaper and far quicker than trading 125 separate contracts. So it is where a view on credit shows up first: what a fund manager buys when they think a recession is coming, and what they sell when they think it is not.

Asset class
Credit derivatives
Instrument type
Index swap on a CDS basket
Traded
OTC, cleared, extremely liquid
Typical users
Credit funds, banks, macro traders

Which risks decide the outcome

Not how risky this is, and not a rating — there is deliberately no total. It says which of five failure modes drives what happens here, in the same order on all 129 products so they can be compared. This publication's own reading; see the notice below.

  • Marketdecides it
  • Creditdecides it
  • Liquiditybarely applies
  • Fundingmatters
  • Operationalmatters

What decides it here. The liquid instrument in a slow market, so it moves first and can overshoot the cash bonds it stands in for.

What the five mean, and which one decides where →

3 · IntermediateHow it works in practice

How the machinery runs

  • The roll: every March and September a new "series" starts with an updated constituent list (fallen angels out, new names in). Liquidity concentrates in the on-the-run series.
  • Fixed coupons: 100bp (IG) / 500bp (HY) running, difference settled upfront — same convention as single names.
  • Defaults: when a constituent has a credit event, its slice pays out via auction and drops from the index; the contract continues on the survivors with reduced notional.
  • Versions: HY trades on price (like a bond), IG on spread — a market-convention quirk.

The ecosystem on top

  • Index options ("swaptions on credit"): payers/receivers on the index — the liquid market for credit volatility and crash hedges.
  • Tranches: the index sliced into loss layers (0–3%, 3–7%, …) — standardised synthetic CDOs that trade correlation.
  • The skew: index spread vs. the average of its constituents' single-name spreads; arbitrageurs trade the difference.
Worked example: a fund with €500M of IG bonds fears a selloff but doesn't want to dump bonds. Buy protection on €300M iTraxx Main at 60bp: cost €1.8M/year. Spreads gap to 110bp in a selloff → index mark-to-market gain ≈ 50bp × 4.5 (duration) × €300M ≈ €6.75M, offsetting much of the bond damage.
4 · AdvancedPricing & valuation

Pricing and the intrinsic skew

The index's fair value is the duration-weighted aggregate of constituent hazard curves; deviations define the skew:

$$ \text{skew} \;=\; s_{index} - \frac{\sum_i \text{RPV01}_i\, s_i}{\sum_i \text{RPV01}_i} $$
What the symbols mean
  • nhow many periods, or how many things

Persistent skew reflects macro-flow demand for the index vs. idiosyncratic pricing of names, plus transaction-cost bounds on the arbitrage (trading 125 names). Skew trades package the index against a replicating single-name portfolio.

Index options

Quoted on forward spread/price with Black-style models; the subtlety is front-end protection — the option must account for defaults between trade and expiry (the "no-knockout" feature), handled via the FEP adjustment. The credit vol surface's skew prices systemic gap risk, and its steepness is a monitored stress indicator.

Tranche correlation

Tranches on the index reprice the loss distribution's shape: equity tranches long idiosyncratic risk/short correlation, seniors the reverse. The market quotes base correlations per detachment; their movement decomposes market moves into "average spread" vs. "systemic-ness". The 2005 correlation unwind and 2012's "London Whale" (massive IG9 tranche positions) are the market's cautionary tales.

Risk usage

Index CS01 hedges portfolio beta cheaply, but leaves single-name basis and curve residuals — quantified via regression hedge ratios (empirical beta of portfolio spread to index spread, typically > 1 in selloffs).

The formulas above are standard textbook formulations, simplified for teaching. They explain the mechanism — they are not a valuation tool, and they will not reproduce a dealer’s price.

5 · Desk notesHow practitioners think about it
Practitioner note: watch the index-option skew and the on-the-run/off-the-run roll cost — both are early-warning gauges that often move before cash credit does.

Now say it back

Close the page and give CDS Index in four sentences. It takes a minute and it is the only way to find out whether reading it was enough.

  1. Who wants what — two parties wanted opposite things badly enough to write it down.
  2. What the contract obliges, and when — not the payoff; the obligation.
  3. Where the money comes from — name the source, or you have described a hope.
  4. What makes it lose — the ordinary way, not the dramatic one.

Do it with a clock → · why these four

Put CDS Index beside any other instrument →

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A bond with a CDS hidden inside: earn an enhanced coupon for carrying someone else's default risk.
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CLO

Leveraged corporate loans, tranched into everything from AAA paper to private-equity-style equity.
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Asset Swap

A bond with its interest-rate risk surgically removed, leaving pure credit. The package that turns any bond into a floating-rate note and defines the spread the market quotes.

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Information and education only. Every page, figure and calculator on this site exists to explain how financial instruments work. Nothing here is investment, tax or legal advice, a recommendation, or a valuation you can rely on. Full disclaimer