Charm flows are the dealer hedging trades driven by charm — delta decay as time passes. They strengthen into the 4pm close, where they can pin price to heavy strikes (the end-of-day pin).

The mechanism

As expiration nears, options’ deltas drift toward 0 or 1.0 (charm). Dealers hedging that drift must trade to stay neutral, and near a big strike this hedging tends to counteract moves — buying dips toward the strike, selling rips away from it — which pins price. On a heavy 0DTE or OPEX day, charm flow can dominate the last hour.

Why it produces the pin

The strike with the most open interest becomes a magnet: charm-driven hedging concentrates there, and in a positive-gamma environment the effect is amplified (dealers damp volatility). The result is the familiar drift-and-stick into 4pm — low-conviction, range-bound, magnetized to a round number.

Charm flow is the reason the last hour so often refuses to trend: dealers bleeding off delta quietly pin price to the heaviest strike into the bell.

What it means for a scalper

Charm flows explain why the close is often a pinning grind rather than a trend, and why holding 0DTE into it is treacherous. Recognize a forming pin (price magnetized to a heavy strike) and trade accordingly — fade toward it while it holds. Its volatility-based counterpart is vanna flow.