Valuation of Interest Rate Derivatives › The Volatility Surface for Interest Rate Options

Michael BrenndoerferDecember 8, 20254 min read
Quantitative FinanceAll chapters
Part 7 of 15Interest Rate Models and Derivatives
Chapter 40Valuation of Interest Rate Derivatives › The Volatility Surface for Interest Rate Options
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Just as equity options exhibit volatility smiles and surfaces, interest rate options display complex volatility patterns across both strike and expiry dimensions.

Cap Volatility Structure

Cap volatilities are typically quoted across a matrix of strikes and expiries. The at-the-money forward (ATMF) strike corresponds to the current forward swap rate for each cap tenor. Volatilities are then quoted at various strike offsets from ATMF.

Out[25]:
Visualization
Three-dimensional surface plot of cap implied volatility, with expiry from 0.5 to 10 years, strike offsets from minus 100 to plus 100 basis points, and a U-shaped volatility smile that rises slightly with expiry.
Interest rate cap implied volatility surface showing how volatility varies across strike offsets (moneyness) and option expiry. The surface typically shows higher volatilities for longer-dated options and exhibits smile patterns at each expiry.

Swaption Volatility Cube

Swaption volatilities form a three-dimensional structure, varying by option expiry, underlying swap tenor, and strike. This volatility cube is fundamental to pricing and risk management in the rates market.

Market makers quote swaption volatilities in matrices such as:

Expiry \ Tenor2Y5Y10Y
1M45.2%38.1%32.5%
6M42.8%36.5%31.2%
1Y40.5%35.2%30.1%
5Y32.1%28.9%26.5%

The pattern typically shows higher volatilities for shorter-expiry options and shorter-tenor underlyings. This reflects the mean-reversion tendency of interest rates: longer-horizon rates exhibit less percentage volatility because they're anchored by long-term expectations.

Out[26]:
Visualization
Heatmap of swaption implied volatilities with option expiry on the y-axis from 1 month to 10 years and swap tenor on the x-axis from 1 to 30 years. Every cell is annotated, and values decline from 52% in the short-expiry, short-tenor corner to 23.5% in the long-expiry, long-tenor corner.
Swaption volatility matrix heatmap showing implied volatilities across different option expiries (rows) and underlying swap tenors (columns). Shorter expiries and shorter tenors typically exhibit higher volatilities, which reflects the mean-reverting nature of interest rates.