Gamma as the Rate of Change of Delta

If delta measures an option’s speed relative to the underlying, gamma measures its acceleration — specifically, how much delta itself changes for a one-point move in the underlying. An option with high gamma will see its delta shift rapidly as the underlying moves, meaning the option’s sensitivity to further price changes is itself unstable and evolving in real time, rather than remaining roughly constant the way it does for low-gamma options.

Where Gamma Is Highest

Gamma peaks for at-the-money options and is close to zero for options deep in or out of the money. This makes intuitive sense: an at-the-money option’s fate is genuinely uncertain, so small price moves cause large shifts in the probability of finishing in the money, which is exactly what delta represents — hence delta changes fast, and gamma is high. Deep in-the-money or out-of-the-money options already have delta near its extreme (close to 1, -1, or 0), leaving little room for further change.

Gamma Increases as Expiry Approaches

One of the most important practical facts about gamma is that it grows sharply for at-the-money options as expiry nears. In the final day or two before expiry, an at-the-money Nifty option’s delta can swing from near 0.20 to near 0.80 within a single session on a moderate move in the underlying — a level of instability that simply does not exist for the same strike three weeks before expiry. This is why expiry-week option trading feels categorically different from trading options with a month of remaining life.

Long Gamma vs Short Gamma

Option buyers are long gamma: as the underlying moves in their favour, their position’s delta increases in the favourable direction automatically, accelerating gains — a genuinely attractive property, offset by the fact that buyers also pay time decay for it. Option sellers are short gamma: as the underlying moves against them, their position’s delta moves against them at an accelerating rate too, meaning losses on short option positions can grow disproportionately fast once the underlying approaches the short strike, particularly close to expiry.

Why Gamma Makes Selling Options Riskier Near Expiry

This accelerating-loss property of short gamma is the central reason many experienced option sellers reduce size or avoid holding short at-the-money positions into expiry day itself. A position that looked comfortably out of the money the previous evening can become dangerously close to at-the-money after a single sharp move, and because gamma is elevated in expiry week, the resulting delta shift — and therefore the p&l swing — happens far faster than the same scenario would produce with two weeks of time remaining.

Gamma Scalping: Trading the Greek Directly

Some sophisticated traders run strategies specifically designed to profit from gamma, known as gamma scalping. A long-gamma position — typically a long straddle or strangle — is delta-hedged with the underlying, and as price moves, the position’s delta shifts automatically, requiring the hedge to be adjusted; done correctly, each adjustment locks in a small profit, effectively monetising volatility itself rather than direction. This is primarily an institutional and professional strategy given the transaction costs involved, but understanding the concept clarifies what gamma really represents.

Gamma Exposure at the Market-Wide Level

Beyond individual positions, aggregate gamma exposure across all option market participants influences index behaviour itself. When option dealers are collectively net short gamma at certain strikes — often near heavily traded round numbers — their hedging activity can amplify moves toward those strikes as they buy into rallies and sell into declines to stay hedged. This dynamic is part of why certain strikes act as unusually strong magnets or barriers on Nifty and Bank Nifty, particularly during expiry week.

Practical Gamma Awareness for Retail Traders

Most retail traders will not actively gamma-scalp, but understanding gamma still changes practical behaviour: it explains why at-the-money option premiums can swing so violently in the final sessions before expiry, why short option positions near the money deserve smaller size and tighter monitoring in expiry week, and why option buyers sometimes see disproportionately large gains from moves that occur close to expiry compared to identical moves that occur weeks earlier.

Gamma and Position Sizing

Because short gamma positions can move against a trader faster than intuition suggests, sound risk management treats expiry-week short options with materially smaller size than the same strategy carries with more time remaining, even if the premium collected looks attractive. The elevated gamma is compensation for genuinely elevated, accelerating risk — not free money — and position sizing should reflect that reality rather than simply chasing the higher premiums that expiry week typically offers.

The Bottom Line

Gamma is the Greek that explains why option behaviour near expiry feels so different from option behaviour with weeks of time remaining — it is the acceleration hiding underneath delta’s speed. Understanding gamma, even without actively trading it, helps explain expiry-week volatility, clarifies why short option sellers should manage risk more tightly near the money, and rounds out the picture that delta alone cannot provide.