Estimating Italian BTP Z-Spreads Against Reference Curves

Summary

The question asks how to obtain a zero-coupon curve for Italian government bonds in order to calculate Z-spreads, including how to treat a bond’s next coupon date. The answer clarifies that the “z” in Z-spread refers to zero volatility, rather than identifying a particular zero curve. It explains that, in the convention described, German sovereign debt is commonly treated as credit risk free while Italian and other sovereign issuers may carry credit risk.

For a Z-spread comparable to Bloomberg’s, the answer proposes numerically finding the parallel shift to the euro swap curve that makes discounted bond cash flows equal the observed bond price. It also suggests comparing the bond’s yield curve with the German government bond curve as an alternative credit-spread perspective. The response does not provide a curve-building procedure, market data, or calculation for the example bond. It distinguishes the spread concept from the original question’s assumption that a standalone Italian zero curve is required.

Key ideas

• The “z” in Z-spread refers to zero volatility, not to a zero-coupon curve.
• A common convention treats German sovereign debt as credit risk free and other sovereign debt as credit risky.
• A Z-spread can be estimated by shifting the euro swap curve until discounted cash flows match the bond price.
• Comparing Italian and German bond yield curves is presented as an alternative way to assess relative spreads.
• The answer does not show the numerical calculation or explain how to construct an Italian zero-coupon curve.

Tags

# How to calculate zero-coupon curve for Italian BTPs?


# How to calculate zero-coupon curve for Italian BTPs?












On the BTP curve, we have the following Bonds (just showing you an extract)

I want to calculate z-spreads my self therefore I need the zero-coupon curve.

How do I go about doing this? Do I look at the yields on the strip curve on Bloomberg? For instance, if we take the BTPS 0.05 01/15/2023, next coupon date is 15th of Jan. How do I calculate the zero-coupon rate for this expiry?

Thank you

## Answer by Dimitri Vulis (score 2, accepted)

https://quant.stackexchange.com/a/68231

Many countries issue sovereign debt denominated in EUR. The common (but not universal) methodology is to treat only German sovereign debt as credit risk free, and all other countries as credit-risky. Italy is one of the PIIGS, but French or (non-EU) Romanian debt is credit-risky too. They're similar to corporate bonds.

The "z" in "z-spread" stands for "zero volatility", not "zero curve". If you're trying to calculate a "Z-spread" similar to Bloomberg's, then you can calculate (numerically) how much the EUR swap curve needs to be shifted in parallel in order for the bond cash flows discounted with the shifted swap curve to match the bond price.

Alternatively, you can compare you bonds' yield curve to German bonds' yield curve.

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