The aggregate delta decay across all options in a dealer hedging book. Creates flows as dealers adjust hedges to match changing deltas near expiration.
⚡ KEY TAKEAWAY: Charm flows are most visible near expiration. Explains otherwise puzzling end-of-day drift in index stocks.
Why It Matters
Charm exposure is the aggregate delta decay across all options in dealer books. Near expiration, deltas shift as options approach expiry — creating systematic flows as dealers re-hedge. These charm flows explain otherwise puzzling end-of-day drift, especially on monthly expirations.
How It Works
Sum the charm (∂Δ/∂t) across all dealer-held options at each strike. As time passes, OTM option deltas decay toward zero — dealers who hedged those deltas must unwind. If dealers were short OTM puts and hedged by selling stock, charm unwind means they BUY stock back — creating upward pressure.
Example
Wednesday before monthly expiration. Dealers are short 50,000 SPY OTM puts with aggregate charm of +800 delta per day. Over the last 3 days, those put deltas fade toward zero — dealers unwind $800 × $580 × 3 = ~$1.4M of stock hedges. This buying pressure drifts SPY upward into expiration.
Common Mistakes
Expecting charm flows to dominate in all environments. Charm flows are visible in calm markets near expiration. During high-vol events (earnings, Fed), directional moves overwhelm charm effects. Charm is a calm-market phenomenon.
The aggregate delta decay across all options in a dealer hedging book. Creates flows as dealers adjust hedges to match changing deltas near expiration.
Why does Charm Exposure matter for premium sellers?
Charm flows are most visible near expiration. Explains otherwise puzzling end-of-day drift in index stocks.
How does Charm Exposure work?
Sum the charm (∂Δ/∂t) across all dealer-held options at each strike. As time passes, OTM option deltas decay toward zero — dealers who hedged those deltas must unwind. If dealers were short OTM puts and hedged by selling stock, charm unwind means they BUY stock back — creating upward pressure.
What are common mistakes with Charm Exposure?
Expecting charm flows to dominate in all environments. Charm flows are visible in calm markets near expiration. During high-vol events (earnings, Fed), directional moves overwhelm charm effects. Charm is a calm-market phenomenon.
