Option gamma

Gamma is the Greek that measures how quickly an option's delta changes when the underlying moves. If delta is the speed of the option's price, gamma is the acceleration.

Change in delta ≈ gamma × change in underlying

Suppose a NIFTY call has delta 0.50 and gamma 0.001. If NIFTY rises 100 points, delta grows by about 0.001 × 100 = 0.10, to 0.60. The next 100 points then add about ₹60 to the call instead of ₹50. That growing sensitivity is why option payoffs bend rather than run in a straight line.

Where gamma is highest

Gamma depends on two things: how close the strike is to the price and how much time is left.

• At the money: gamma peaks where the strike is nearest the price. Deep in-the-money and far out-of-the-money options have little gamma, because their deltas are already close to 1 or 0 and cannot change much.
• Near expiry: ATM gamma rises sharply as time runs out. With a week left, a small move barely changes whether the option ends in the money. With an hour left, a 50-point move can decide it completely.
• Low implied volatility: lower IV concentrates gamma around the ATM strike; higher IV spreads it across more strikes.

A worked example: one week vs one day

Take NIFTY at 25,000 and IV at 13% (illustrative numbers worked out with the usual pricing model):

With a day left, the same 200-point move pushes the call almost to a delta of 0.9: it now moves nearly point for point with NIFTY, and its price can triple. That is gamma at work, and it is why expiry-day option prices swing so violently. See the expiry day guide.

Long gamma and short gamma

Buyers of options are long gamma. When the market moves their way, delta grows and gains accelerate. When it moves against them, delta shrinks and losses slow down. Big moves in either direction help a long straddle.

Sellers of options are short gamma. When the market moves against a short option, its delta grows against the seller, so each extra point costs more than the last. A short straddle that loses ₹2,000 on the first 100 points can lose much more on the next 100. This is gamma risk, and it is the main danger of selling options near expiry.

Gamma and theta: two sides of one trade

Gamma never comes free. Options with high gamma also have high theta. An ATM option on expiry day decays fast, which is what sellers earn; in exchange, they carry the most gamma risk. The buyer pays that decay for the chance of a fast move.

• If the market moves more than the options priced in, gamma wins: buyers profit.
• If the market moves less, theta wins: sellers profit.

You can watch this contest on the straddle chart. A falling line means theta is winning; a sharp rise means gamma is:

Compare the day high and the day low with the time they happened. A big jump late in the day, close to expiry, is usually gamma: NIFTY moved away from the strike when there was little time value left to cushion it.

Gamma across the whole market

Gamma matters beyond single trades. When option sellers as a group hold a lot of short gamma at certain strikes, their hedging can push NIFTY around. Dealers who are long gamma tend to sell into rallies and buy dips, which calms the market; when they are short gamma, their hedging can make moves bigger. The site estimates where these levels sit from open interest:

The call wall and put wall are the strikes with the heaviest gamma; the zero-gamma level is roughly where the market's overall gamma switches sign. These are estimates built on assumptions about who holds which options, explained in the gamma exposure guide. Treat them as areas to watch, not as hard barriers.

Gamma in rupees for a real position

Gamma per unit looks tiny, so it helps to turn it into rupees. Suppose a trader has sold one lot of the NIFTY 25,000 straddle with a day left, and assume a lot size of 75 units (check the current figure on NSE). The straddle's combined gamma is about 2 × 0.0023 = 0.0046 per unit, or about 0.35 for the lot. For the seller it is negative.

• After a 100-point move, the position delta has shifted by about 35 units against the seller. The next 100 points then cost roughly ₹3,500 more than the first 100 did.
• After a 200-point move, the shift is about 70 units, and losses are now growing almost as fast as an outright futures position.

The same position a week before expiry would have about 40% of that gamma, so the same move would hurt much less. This is why many sellers reduce size, widen their strikes or buy protective wings as expiry approaches.

How traders use gamma

• Choosing expiries: a buyer who expects a large move soon may accept the higher decay of a near expiry for its higher gamma; a seller who wants calmer risk may prefer a later expiry with lower gamma.
• Sizing near expiry: because gamma rises so fast, a position that felt small on Monday can be large on expiry day.
• Capping risk: buying a far call and a far put against a short straddle (an iron butterfly) limits how far gamma losses can run.

Gamma scalping

Professional traders who are long gamma sometimes gamma scalp: they buy options, hedge delta with futures, and then rebalance as the market moves. When NIFTY rises, their delta grows and they sell futures; when it falls, they buy futures back. Each round trip locks in a small gain. It pays only if the market moves enough to cover the theta they pay each day and the trading costs. For most retail traders, frequent rebalancing costs make this hard.

Common mistakes

• Selling ATM options on expiry day without a stop. Gamma is at its peak; a quick 1% move can wipe out weeks of small gains.
• Thinking far OTM options are safe to sell because their gamma is low. Gamma rises sharply as the price approaches the strike, so a far option can quickly become a near one.
• Ignoring position size. Gamma per unit looks tiny (0.001). Times lots and lot size, it can mean a large change in exposure for each 100 points.
• Reading gamma levels as certain support or resistance. They are estimates and can break on news.