How delta hedging by market makers shapes intraday realized volatility — and why one number on the dashboard can tell you whether to fade extremes or follow breakouts.
delta is the slope, gamma is how fast the slope itself changes
Delta ($\Delta$) is the first derivative of an option's value with respect to the underlying — how much the option's price moves for a $1 move in the stock.
Gamma ($\Gamma$) is the second derivative — the curvature. It tells you how fast delta itself is changing.
An ATM option has the highest gamma — small spot moves cause big delta swings, which forces dealers into the most hedging activity.
market makers do not take directional bets — they neutralize delta with the underlying
When a market maker sells 1,000 ATM calls with $\Delta \approx 0.55$, they immediately short 550 shares of the underlying to cancel out the directional exposure.
The dealer's P&L is now insensitive to small moves in $S$ — they earn the bid-ask spread on the option, not a directional bet.
But this hedge only works for an instant. As $S$ moves, $\Delta$ changes — and the hedge must be rebalanced. That's where gamma comes in.
a 1-point move in S forces the dealer to trade Γ · OI · 100 shares to stay flat
As $S$ moves by $\Delta S$, dealer delta shifts by $\Gamma \cdot \Delta S$. To stay neutral, they must trade that many delta-equivalent shares:
High $|\Gamma|$ ⇒ constant rebalancing. The direction of that rebalancing — whether dealers buy on rallies or sell on rallies — depends on whether they're net long or net short gamma.
retail buys premium, so dealers are usually short gamma in heavily-traded names
price ↑ → dealer SELLS shares · price ↓ → dealer BUYS. Profits from realized vol. Trades counter-trend. Supplies liquidity. Stabilizes the market.
price ↑ → dealer BUYS shares · price ↓ → dealer SELLS. Loses to realized vol. Trades with the trend. Drains liquidity. Amplifies moves.
aggregate dealer dollar-gamma summed across the whole option chain
Summed across every strike on every expiry, weighted by open interest:
$s_i = +1$ for calls, $-1$ for puts · units: dollars of dealer hedging required per 1% move in S.
Positive total ⇒ dealers stabilize (long gamma). Negative total ⇒ dealers amplify (short gamma).
the strike where dealer gamma flips sign — your single best regime indicator
Plotting cumulative dealer GEX as a function of spot, the curve crosses zero at one strike — the gamma flip level.
Above the flip: dealers are net long gamma → vol compresses, mean-reverting day.
Below the flip: dealers are net short gamma → vol expands, trending day.
Your day-trading playbook should look at distance from the flip, not the absolute GEX number.