How much Delta changes when Implied Volatility changes (it is also the change in Vega when price moves). It explains why a market maker's hedge shifts as fear rises or calms, even when the stock barely moves.
What it measures
Vanna (Vanna) is a second-order Greek that measures how Delta changes when Implied Volatility changes (or how Vega changes when price moves; the two views are equivalent). In plain words: how much does your directional exposure shift when fear rises or fades?
Why it moved from the textbooks to the screens
It explains "fear fading" rallies. When implied volatility drops after an event passes safely, the delta of the protective puts that hedgers hold shrinks. The dealers hedging against them then find themselves buying the market mechanically to rebalance. It is a mechanical rise fueled by falling fear, not by new news.
Its best-known window
Vanna and Charm flows are clearest in the weeks before major expirations. The existing hedge book is huge, and every quiet day that passes (Charm) and every point of fear that drains (Vanna) pulls in mechanical buying. A seasonal "tailwind" that structure readers know well.
Hypothetical example
The market gets through a rate meeting safely. Implied volatility collapses from 22 to 16 in two days, and the market grinds higher despite lukewarm news. Vanna flow is at work: protection loses its delta, so its hedges get unwound by buying. Anyone who did not know the mechanism called it "a rally for no reason".
Common mistake
Hunting for Vanna every day: its effect usually drowns in noise and becomes a dominant driver only when the hedging structure is swollen and the fear premium is draining at the same time. It is a context tool, not a timing trigger.
Where to see it on the platform
The Gamma panel shows an estimate of Vanna flows among the structural forces, and the learning pages explain its mechanism with charts.
