Commodity and Inflation Swaps · Swaps Trading Guide

Inflation contracts use specific index months, lags and sometimes interpolation. Those details can matter as much as the quoted rate.

The observation month may precede payment

Price indexes are published after their reference periods. An inflation swap can therefore use an index with a contractual lag. A payment in June need not use June inflation. Read the designated index months and fixing rules before comparing a payment with the latest published annual inflation figure.

Distinguish interpolation from estimation

Some contracts interpolate between monthly index levels using a specified calendar formula. This is a contractual calculation, not an analyst forecast. For an illustrative halfway interpolation between 120 and 121, the level is 120.5. Actual contracts define the weights, index availability and relevant dates precisely.

Keep seasonality in the right place

Monthly price levels can show seasonal patterns. A short dated inflation calculation can be sensitive to the specific start and end months, even when the long term inflation view is unchanged. Do not replace an unadjusted contractual index with a seasonally adjusted series merely because its chart looks smoother.

Handle revisions and disrupted indexes

Confirm whether the contract uses the initially published index or another specified version. Index changes, delayed publication and discontinuation can require fallback provisions. A reliable model stores the exact index identifier, reference month and publication version alongside the value, so historical payments can be reconstructed.

Try it yourself

A simplified interpolation assigns 25% to an index level of 104 and 75% to 106. What level results?

Show the worked answer

The result is 105.5. This weighted index level must still be compared with the correct contractual base index. It is not an annual inflation percentage by itself.

Further reading

Educational material, not a recommendation to transact. Numerical examples are hypothetical and simplify contract terms. Access, documentation, collateral and regulatory requirements depend on the product, jurisdiction and counterparties.

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