What traders mean by a gamma blast

The phrase

"Gamma blast" is Indian trader slang for a sharp move on or just before an expiry day, when cheap out-of-the-money options suddenly gain many times their price. The term describes the option buyer's experience of the move. It is not an exchange term and it is not something a model can detect in advance.

Why gamma is largest near expiry

Gamma measures how fast an option's delta changes as the index moves. For an at-the-money option it grows roughly with one over the square root of the time left, so in the last session before expiry it is several times larger than a week out. A small index move can then turn a far cheaper option into an in-the-money one within minutes.

Whoever is short that gamma has to hedge faster as the move extends: under the "writers short every option" reading, the hedging flow runs in the direction of the move. That is the mechanism traders usually mean.

What end-of-day data can and cannot show

It can show, the evening before an expiry, how much gamma is concentrated near the money, where the walls sit and how the net exposure reads under each sign convention. It cannot show what happens during the session: open interest moves through the day and these numbers do not.

Nothing on this page says a large move will happen. Expiry days with heavy near-the-money gamma often end quietly too.

Nifty before its nearest expiry

Nearest expiry 13 Oct 2026, 5 days after the 8 Oct 2026 close. Net GEX ₹11,166 cr per 1% move with dealers long calls, -₹1,05,303 cr with writers short every option. Call wall 22,500, put wall 22,000.

A description of positioning at the close, not a prediction of the expiry-day range. Full Nifty levels.