Volatility Targeting: Why Your Index Isn't as Stable as You Think

中文标题

波动率目标策略：为何你的指数并不像你以为的那样稳定

Nomura Connects10/22/2026updated 10/22/2026

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Citable research brief

Core conclusion · Tlines extraction

Nomura research published in Mathematical Finance shows that volatility targeting indices realize volatility systematically above their stated target, usually by more than 10% on a relative basis. Multipliers U(λ) and V(λ) always exceed 1, so faster rebalancing does not converge to the target but to an inflated level; with decay parameter λ=0.9, V is about 1.1 or higher. A vega conversion formula links underlying volatility sensitivity to rate sensitivity for pricing and hedging.

Institution: Nomura Connects
Published: 10/22/2026
Research topic: Not explicitly stated
Time horizon: Not explicitly stated

Key arguments

The realized volatility of volatility targeting indices is consistently higher than the indicated target, typically by more than 10% relative.
As rebalancing frequency rises toward zero, volatility converges to a level scaled by multipliers U(λ) and V(λ), both greater than 1, not to the target.
A vega conversion formula translates volatility sensitivity on the underlying into rate sensitivity on the limiting diffusion, correcting the common assumption that vega exposure is negligible.
Window size for historical variance estimation and rebalancing frequency have a subtle competing effect that practitioners must manage.

Key numbers

Typical relative excess of realized volatility over target: more than 10%
Volatility multiplier V(λ) at decay parameter λ=0.9: approximately 1.1 or higher
Implied underestimation of true volatility at λ=0.9: at least 10%

Main risks

Risk managers using these indices as a low-risk sleeve are likely underestimating reported risk.
Traders assuming vega exposure on these indices is negligible may misprice and mishedge options.
The results are theoretical limiting-distribution findings; realized outcomes depend on parameter choices such as window size and rebalancing frequency.

Corresponding source evidence

Michel Gauthier Managing Director Xuan Liu Vice President Our research shows that volatility targeting indices have consistently higher volatility, usually more than 10% on a relative basis, than the indicated target level.
Intuitively, this should keep portfolio volatility constant at a preset level, say 10% annually.
Both are consistently greater than 1, meaning realized volatility always exceeds the target.

Context: the conclusion is Tlines' automated extraction, not the institution's wording. Quoted evidence is publisher wording. Scope and date must travel with the conclusion.

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