A gamma blast is what Indian traders call a cheap option suddenly multiplying in value, usually in the last hours before expiry: a ₹5 put that is worth ₹80 by the close, or a call that goes from ₹3 to ₹60 in an afternoon. It is real, and it is mechanical. It comes from gamma, the measure of how fast an option’s sensitivity to the index changes, which becomes enormous for options near the money as expiry approaches. The same mechanics explain the other side of the story, which gets talked about less: on most expiry days those cheap options go to zero. This guide explains what a gamma blast is, why gamma explodes on expiry day, walks through a real one from 15 September 2026, and shows the part played by dealers’ hedging and by the closing auction.
What a gamma blast is
Take an out-of-the-money option on expiry morning. It has no intrinsic value, only a little time value, so it is cheap. If the index then moves through the strike, the option gains intrinsic value point for point, and a contract that cost a few rupees can be worth tens or hundreds by the close. Measured from its low, the gain can be ten, twenty or thirty times. That multiplication is the gamma blast. Buying such options as a lottery ticket on expiry day is what traders call a hero-zero trade: the option either becomes a hero or goes to zero.
Why gamma explodes on expiry day
Delta is how much an option’s price moves for a one-point move in the index. An option far out of the money has a delta near 0; one deep in the money has a delta near 1 for calls or −1 for puts. Gamma is how fast delta changes as the index moves.
With plenty of time left, delta changes gently. With a week to expiry and NIFTY near 23,000, a 100-point move takes an at-the-money call’s delta from about 0.5 to about 0.6. In the last hour of expiry day there is no time left for the index to come back, so the same 100 points can take that delta from about 0.5 to 0.9 or more. That steepness is gamma, and it is highest at the strike nearest the index and in the final hours. The option Greeks guide explains each of these sensitivities.
The practical result: on expiry afternoon, an option a little out of the money behaves almost like a switch. Below the strike it is worth nearly nothing; once the index crosses the strike it becomes almost a one-for-one position in the index. A move of a hundred points can turn a few rupees into a hundred.
A real gamma blast: NIFTY on 15 September 2026
Tuesday 15 September 2026 was a NIFTY weekly expiry and the first session after the Ganesh Chaturthi holiday on Monday. NIFTY had closed at 23,398.10 on Friday 11 September. It opened 178 points higher at 23,576.15, made its high of 23,592.85 in the first minute, and then slid for the rest of the session: about 23,383 at 10:00, 23,311 at 13:00, 23,202 at 14:30 and 23,172 at 15:00. Continuous trading stopped at 15:15 with the index at 23,172.35, and the closing auction printed the official close at 23,118.60, 474 points below the day’s high.
The expiring puts went the other way. Their prices, from each contract’s own record on Strike History:
| Put strike | Lowest trade on 15 Sept | Settled at | Multiple of the low |
|---|---|---|---|
| 23,300 | ₹6.75 | ₹181.40 | about 27× |
| 23,250 | ₹4.40 | ₹131.40 | about 30× |
| 23,200 | ₹3.10 | ₹81.40 | about 26× |
| 23,150 | ₹2.25 | ₹31.40 | about 14× |
Expiring index options settle at the index’s official close, so each put settled at its strike minus 23,118.60. The calls tell the other half: the 23,300 call opened at ₹294 and expired worthless, as did every call above it. Every rupee the put buyers made was paid by the writers of those puts, and the call buyers had a very bad day as well.
What dealers’ hedging had to do with it
Whoever wrote those puts was short gamma: as the index fell toward and through their strikes, their losses grew faster with every point. A writer who hedges a short-gamma position does it by selling futures as the index falls, and that selling can add to the fall. The previous evening’s reading in OIData had already shown that regime. At the close of 11 September, net dealer gamma for NIFTY was negative, about −₹16,900 crore, with the index at 23,398.10 below a gamma flip of about 23,500, the level below which hedging tends to amplify moves rather than damp them. The put wall, the strike with the most put open interest, was at 23,300, the same strike that went 27 times from its low.
None of that said NIFTY would fall 474 points from its high. It said that if the index did move, hedging would push in the same direction rather than against it. The gamma flip guide and the hedge ladder explain both readings.
The closing auction twist
Look again at the 23,150 put. At 15:15, when continuous trading stopped, NIFTY was at 23,172.35, above its strike, and the put was still out of the money. The closing auction then printed 23,118.60, 53.75 points lower, and the put settled at ₹31.40. That last part of the gamma blast happened in a price the screen did not show until the print. Since the exchanges introduced the closing auction on 3 August 2026, the official close, and with it the settlement of every expiring index option, comes from that auction. The closing auction session guide shows how far the print can land from the frozen value.
Why most hero-zero trades still lose
A gamma blast needs a move larger than the one the market priced, in the right direction, before the close. Most expiry days do not deliver that. OIData’s Expiry Day page counts how often NIFTY finished inside the morning band, spot plus and minus the opening at-the-money straddle: in eight of the last eleven expiries before 6 October 2026, it did. On those days, options outside the band went to zero.
The price of a cheap option already reflects the small chance of a big move. Its delta is a rough guide to that chance: an option with a delta of 0.05 finishes in the money about one time in twenty. Buying such options again and again is a run of small losses broken by occasional large wins, and nothing guarantees the wins cover the losses. The regulator’s own numbers are sobering. In SEBI’s study of individual traders, published in August 2026, 87.7 percent of individuals trading equity derivatives lost money in FY26, options made up 92 percent of their losses, and 59 percent of index options turnover happened on the expiry day itself.
Reading expiry-day gamma in OIData
- The Expiry Day page shows the pin funnel with gamma at spot, pin probability and magnet pull, the expected-move band with its morning range and how many past expiries closed inside it, the at-the-money straddle’s decay against its model, and premium decay strike by strike.
- Dealer Positioning shows net gamma exposure, the regime, the gamma flip, the walls and the hedge ladder through the session, with the regime’s history day by day.
- The Session Chart draws the gamma flip, the walls and the pin on the candles, so a break through them is visible as it happens.
- Options Activity flags strikes whose volume bursts far above their own normal, which on expiry afternoons is often where cheap options are being bought.
Gamma blast FAQ
What is a gamma blast? A cheap, out-of-the-money option multiplying in value when the index moves through its strike close to expiry, because gamma, the rate at which its delta changes, is at its highest then.
When does a gamma blast happen? Most often on expiry afternoons after a sustained move in one direction, when options near the money switch from almost worthless to in the money within a few dozen points.
Can a gamma blast be predicted? The conditions can be seen: negative dealer gamma, the index below the gamma flip, a wall close to spot, cheap options near the money. The move itself cannot. Most expiry days end inside the range the options priced in the morning.
What is a hero-zero trade? Buying cheap out-of-the-money options on expiry day in the hope of a gamma blast. The option either multiplies or expires worthless, and the second outcome is the more common.
Is a gamma blast the same as a gamma squeeze? They are related. A gamma squeeze usually describes dealers’ hedging pushing the underlying further; a gamma blast describes what that move does to the price of the cheap options themselves.
Takeaways
- A gamma blast is an out-of-the-money option multiplying when the index crosses its strike near expiry; gamma is what makes the switch so abrupt.
- On 15 September 2026 NIFTY fell 474 points from its high, and expiring puts rose 14 to 30 times from their lows; the 23,300 call expired worthless.
- Negative dealer gamma below the flip had set up an amplifying tape; the closing auction print added the last 54 points.
- Most expiry days end inside the morning band, and most cheap expiry-day options expire at zero.
- Watch gamma at spot, the regime and the walls on the Expiry Day and Dealer Positioning pages; they show the conditions, never the outcome.