Gamma Explained:
The Greek Behind Delta

What is gamma?

If you have read the delta explained guide, you know that delta measures how much an option's price changes for a one-point move in the underlying. But delta itself is not fixed — it shifts as the underlying moves. Gamma is the rate of change of delta: it tells you how much delta will increase or decrease when the underlying moves by one point.

Formally: if NIFTY moves up by 1 point, the new delta ≈ old delta + gamma. Because gamma is always positive for option buyers (both calls and puts), buying options always makes you more directional as the underlying moves in your favour, and less directional as it moves against you. This asymmetry is the structural advantage buyers pay for through time value.

Gamma and the delta curve

Think of delta as a position on an S-curve that runs from 0 (deep OTM) to 1 (deep ITM) for calls. The slope of that curve at any point is gamma. The slope is steepest at the money — gamma is highest for at-the-money options and falls away as the option moves deep ITM or far OTM.

That peak near ATM has a critical implication: a small price move around the ATM strike causes the largest delta shift. This is where gamma risk concentrates, and it is the reason ATM options on expiry day behave so explosively.

Long gamma vs. short gamma

Every option position is either long gamma or short gamma:

• Long gamma (option buyer) — your delta grows in the direction of the move. If you buy a NIFTY call and NIFTY rallies, your delta accelerates upward. If NIFTY falls, your delta shrinks, limiting your loss. You pay for this through time value decay (theta).
• Short gamma (option seller) — your delta works against you as the move extends. A short NIFTY straddle sees its delta flip more and more wrong as the underlying trends. Sellers collect theta but are exposed to explosive losses from large moves.

This trade-off between gamma (curvature benefit for buyers) and theta (time decay received by sellers) is the central tension in options pricing. You cannot have both — you either pay time premium to own the curvature, or you collect it and carry the gamma risk.

Why gamma explodes near expiry

On a monthly expiry, an ATM NIFTY option might have a gamma of 0.0005. On the morning of weekly expiry, that same ATM option can have gamma ten times higher. Here is why: with almost no time left, even a tiny move in NIFTY can swing the option from worthless (expires OTM) to full intrinsic value (expires ITM). Delta must therefore react violently to each point of price movement — and that violent reaction is high gamma.

For option sellers running weekly strategies like short straddles or iron condors on Bank Nifty (lot size 15) or NIFTY (lot size 75), Thursday expiry morning is when gamma risk is most acute. A 100-point gap in either direction can cause delta to flip completely and require urgent hedging.

Gamma exposure across the market

Institutional market makers (who sell options to retail traders) aggregate their gamma positions into a number called gamma exposure (GEX). When total GEX is large and positive, makers are long gamma — their hedging activity (buy dips, sell rallies) dampens intraday volatility. When GEX turns negative, their hedging amplifies moves, which is why sharp trending days often coincide with negative GEX regimes.

TradePulse's option chain analysis page tracks aggregate OI and change-in-OI patterns that reflect these gamma dynamics. The gamma exposure guide goes deeper on GEX interpretation.

A worked NIFTY example

Suppose NIFTY is near 22,500 on a Wednesday afternoon (one day before weekly expiry). Consider a hypothetical ATM 22,500 call:

• Delta: 0.50 | Gamma: 0.008 (illustrative)
• NIFTY rises 50 points to 22,550. New delta ≈ 0.50 + (0.008 × 50) = 0.90
• NIFTY falls 50 points to 22,450. New delta ≈ 0.50 − (0.008 × 50) = 0.10

With one lot (75 units) and a premium of say ₹80 at entry, the buyer's P&L swings dramatically from a 50-point move because delta has near-doubled on the upside. This illustrates why buying ATM options the day before expiry is a high-gamma, high-risk/reward trade — small moves can double or wipe the premium quickly.

Conversely, someone who sold that call is now badly short-delta if NIFTY pops to 22,550. They need to buy futures (or calls at a higher strike) to re-neutralise delta — classic delta hedging.

Common mistakes

• Ignoring gamma when buying far-dated options. Long-dated options have low gamma — delta barely accelerates, so large moves give smaller-than-expected P&L boosts. Buyers expecting explosive gains should check the gamma, not just the delta.
• Selling ATM options the day before expiry without a hedge. Gamma is at its peak; a gap can turn a premium-collecting trade into a large loss before you can react. SEBI's SPAN margin system does partly account for this but does not protect against intraday gaps.
• Treating gamma as constant. Gamma itself changes as the underlying moves — the rate of change of gamma is called speed (third-order Greek). For practical trading, the key insight is that gamma rises as you approach ATM and as expiry nears.
• Confusing gamma with vega. Both are highest near ATM, but gamma responds to price moves while vega responds to IV changes. An IV crush event after earnings hurts vega, not gamma.

Frequently asked questions

What is gamma in options trading?

Gamma is the rate of change of an option's delta for a one-point move in the underlying. If a NIFTY call has delta 0.45 and gamma 0.003, a 100-point rise in NIFTY moves delta to approximately 0.75. It tells you how quickly your directional exposure is shifting.

Why does gamma spike near expiry?

As expiry approaches, at-the-money options have very little time left to resolve. A small move in the underlying can flip an ATM option from worthless to valuable in minutes. This uncertainty makes delta extremely sensitive to price — gamma surges. Deep ITM and OTM options see much smaller gamma because their outcome is already fairly certain.

Is high gamma good or bad?

It depends on whether you are long or short gamma. Option buyers (long gamma) benefit from large, fast moves — gamma accelerates their gains. Option sellers (short gamma) are hurt by large moves — gamma amplifies losses. Short-gamma positions require active hedging or tight stop-losses, especially on weekly expiry days.

What is gamma exposure (GEX) and why do traders watch it?

Gamma exposure (GEX) is the aggregate gamma position of all market makers across all strikes. When GEX is large and positive, market makers are long gamma and tend to dampen intraday moves by buying dips and selling rallies. When GEX is negative, market makers are short gamma and their hedging amplifies moves. TradePulse tracks GEX on the option chain dashboard.

Keep learning

• Delta explained — understand the first-order Greek before gamma
• How the Greeks interact — delta, gamma, theta and vega together
• Theta explained — the time-decay cost of being long gamma
• Gamma exposure (GEX) explained
• Live option Greeks on TradePulse