What is vanna and why do FX option traders monitor it so closely?

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AcadiFi · Accepted Answer

Vanna is a second-order Greek equal to the cross partial of option value with respect to spot and volatility. Equivalently, it measures how delta shifts when implied volatility changes, or how vega shifts when spot moves. For an out-of-the-money call on a currency pair like MXN/USD, a spike in implied vol can push delta from 0.22 up toward 0.31 even without spot moving, and vanna quantifies that drift.

Consider an FX book at a Lisbon dealer called Harborlane Markets holding a short 0.25-delta USD put with vega of 9,500 and vanna of 4,200 per vol point per spot unit. If spot drops 0.8% while vol rises 1.2 points, vanna contributes a delta move of roughly 4,200 times 1.2 divided by notional scaling, meaning the short put is now closer to at-the-money than a pure delta hedge suggests. Ignoring vanna leads to systematic under-hedging during risk-off moves when spot and vol correlate.

FX traders monitor vanna because smile risk is material: the vanna-volga pricing framework explicitly adjusts Black-Scholes prices using vanna, volga, and vega hedges against 25-delta risk reversals and butterflies. For CFA Level II candidates, the key insight is that first-order Greeks assume parameters are frozen, but in practice volatility surfaces twist daily, and vanna captures that twist cost.

What is vanna and why do FX option traders monitor it so closely?

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