Skip to main content

Vanna & Charm Flows

Updated Jun 24, 2026 at 8:22pm

Research Draft High 1,080 words

Vanna and charm are second-order option Greeks that describe how an option's delta changes when two non-price variables move: implied volatility (vanna) and the passage of time (charm). The "flow" idea is that option dealers who run delta-neutral books must mechanically buy or sell the underlying as their aggregate delta drifts from these effects — even when spot itself hasn't moved. The core tension: the math of vanna and charm is exact and uncontroversial, but the market narrative ("vanna rallies," "charm pin into the close") rests on a chain of assumptions about who holds what and in which sign — assumptions that are plausible for index options but far harder to verify than the formulas suggest.

How it's calculated / formed

Both are partial derivatives of the Black-Scholes delta:

  • Vanna = ∂Delta/∂σ = ∂Vega/∂Spot. It measures how much delta shifts per unit change in implied volatility (IV). Vanna is largest for out-of-the-money options with meaningful time to expiry; it is near zero for deep ITM/OTM and for very short-dated contracts.
  • Charm (a.k.a. delta decay or DdeltaDtime) = ∂Delta/∂time. It measures how delta drifts as time passes with spot and IV held fixed. Charm is largest for near-the-money, near-expiry options — exactly the regime that 0DTE and weekly options live in.

The flow narrative aggregates these per-contract Greeks across all open interest, multiplies by a dealer-positioning sign (an assumption about whether dealers are net long or short the options), and reads off the implied hedging direction. Two canonical mechanics:

  • Vanna flow: If dealers are net short index puts (the standard assumption), a decline in IV reduces the puts' delta magnitude, leaving dealers over-hedged short the underlying; to re-neutralize they buy futures. Falling fear → lower IV → dealer buying → higher spot → still-lower IV — the self-reinforcing "vanna rally" or "vol-reset rally" described by vendors such as SpotGamma and by Nomura's Charlie McElligott.
  • Charm flow: As OTM options decay toward zero delta into expiry, the hedges against them are unwound. Under the short-put assumption this again tends to produce buying of the underlying and contributes to the "end-of-day pin" toward high-open-interest strikes, concentrated in the final hours and into monthly/quarterly OPEX.

How it's used in practice

Practitioners use vanna and charm as a positioning lens, not a signal in isolation. Common applications:

  • Calendar context. The "vanna/charm window" — roughly the stretch before monthly OPEX — is framed as a structural tailwind, with the post-OPEX "window of weakness" the period after that hedging support rolls off (a McElligott-popularized framing).
  • Vol-event playbook. After a VIX spike resolves, vanna is cited as the mechanism behind sharp, news-light recoveries as IV mean-reverts.
  • Intraday timing. Charm is invoked to explain Friday-afternoon and into-the-close drift toward dominant strikes, especially in SPX where 0DTE volume is enormous.

Crucially, these are conditioning tools: they describe an environment's likely path-of-least-resistance and fragility, layered on top of a directional thesis from elsewhere.

Adoption, debate & evidence

Adoption has grown rapidly since ~2018–2020, driven by sell-side commentary (Nomura) and retail-facing data vendors (SpotGamma, Perfiliev, MenthorQ, and various "GEX" sites). It is now common vocabulary on financial media.

The honest evidence picture is mixed:

  • Supportive academic work: Barbon & Buraschi (Gamma Fragility, SSRN 3725454, 2021) document that stock-level dealer gamma imbalance interacts with illiquidity to produce intraday momentum (negative gamma) or reversal (positive gamma). This is real, peer-reviewed support for the underlying mechanism — delta-hedging feedback moving the underlying. Note, however, that this paper is about gamma, not vanna or charm specifically; vanna/charm-specific causal evidence in the academic literature is much thinner.
  • The weak link is the sign assumption. Every flow estimate requires assuming dealer net positioning (e.g., "dealers are short puts"). Dealer inventory is not publicly observed; vendors infer it from heuristics. If the assumed sign is wrong, the predicted flow direction flips. SpotGamma itself notes vanna is harder to isolate than gamma because net exposure is an aggregate of many positions.
  • Confirmation-bias risk. Because the narrative is flexible (a "window of weakness" merely means flows aren't supportive), it can be fit to almost any outcome after the fact. "Folklore vs measured": the gamma-feedback channel is measured; the precise, tradeable timing of vanna/charm rallies is largely folklore-grade, with no widely cited out-of-sample return study establishing a standalone edge.

Strengths & limitations

When it works: Most useful in index/ETF options (SPX, SPY, QQQ), where open interest is huge, dealers genuinely intermediate large flow, and aggregate positioning sign is more stable. The clearest real-world fingerprints are the gamma-related ones (pinning, volatility suppression) that have academic backing.

When it fails:

  • Single names — dealer-positioning inference is noisier and OI is thinner.
  • Sign errors — the entire prediction inverts if assumed dealer positioning is wrong.
  • Regime breaks — genuine new information overwhelms mechanical flow; vanna "support" evaporates precisely in a real vol-up cascade.

#1 misuse: treating vanna/charm exposure charts as a directional signal rather than a conditional, positioning-dependent context. A second frequent error is conflating vanna/charm with gamma and borrowing gamma's stronger empirical support — they are distinct Greeks with much weaker direct evidence.

Sources

Disputed/soft claims flagged: the existence and tradeability of "vanna rallies" and "charm pins" are practitioner narratives with limited direct academic verification; only the broader delta-hedging-feedback (gamma) channel is peer-reviewed. All directional flow claims are contingent on unobserved dealer-positioning signs.