What Is Option Gamma? Delta's Accelerator

Gamma is the option greek that measures how fast delta changes. Where delta is the option's speed versus the stock, gamma is its acceleration — how much delta moves for each $1 move in the underlying. It is the reason a calm option can turn explosive: as the stock moves, gamma is what re-shapes the whole position. Two forces drive it, and both show up in real data.

Gamma climbs as expiry approaches

Here is our SPY $740 call's gamma over its final seven weeks:

SELECT date,
       round(avg(gamma), 4) AS gamma
FROM global_markets.options_greeks
WHERE ticker = 'O:SPY260618C00740000' AND date BETWEEN '2026-05-01' AND '2026-06-17'
GROUP BY date ORDER BY date

Gamma did not simply rise — it tracked the strike. It began near 0.0105, ran highest on the days SPY sat right around $740 with only weeks left, and collapsed toward zero once the stock closed well above the strike into expiry and the call turned into a stock substitute. Two forces set gamma, and the SPY board separates them. First, TIME: an at-the-money option's delta reacts more to each move the nearer it gets to expiry, so gamma climbs steeply as the clock runs down:

SELECT multiIf(days_to_expiry<=7,'0-7 days',days_to_expiry<=30,'8-30 days',
               days_to_expiry<=90,'31-90 days','90+ days') AS time_to_expiry,
       round(avg(gamma), 4) AS avg_gamma
FROM global_markets.options_greeks
WHERE date = '2026-07-13' AND underlying_symbol = 'SPY' AND abs(delta) BETWEEN 0.45 AND 0.55
GROUP BY time_to_expiry ORDER BY min(days_to_expiry)

A same-day option carries many times the gamma of a three-month option at the same strike. This is the coiled spring behind a 0DTE trade: near expiration, an at-the-money contract's delta can swing from 0.2 to 0.8 on a small move, and its value lurches with it. It is also the mechanism named in a "gamma squeeze" — dealers short lots of short-dated calls must buy stock as it rises to stay hedged, and that buying pushes the stock higher still, a squeeze that comes from option positioning rather than fundamentals.

Gamma is largest at the money

The second force is moneyness. Fix the expiry and vary the strike, and gamma is a bell centered on the current price:

SELECT multiIf((strike_price/underlying_close-1)<-0.04,'deep ITM',
               (strike_price/underlying_close-1)<-0.015,'ITM',
               (strike_price/underlying_close-1)<0.015,'ATM',
               (strike_price/underlying_close-1)<0.04,'OTM','deep OTM') AS moneyness,
       round(avg(gamma), 4) AS avg_gamma
FROM global_markets.options_greeks
WHERE date = '2026-07-13' AND underlying_symbol = 'SPY' AND option_type = 'C'
  AND days_to_expiry BETWEEN 25 AND 40
GROUP BY moneyness ORDER BY avg(strike_price/underlying_close)

A deep-in-the-money call already moves nearly one-for-one with the stock, so there is little room for delta to change; a deep-out-of-the-money call barely reacts. Only the at-the-money strike sits on the knife's edge, where a small move flips the odds — and that is where gamma concentrates. Combine the two forces and the maximum-gamma option is the one that is at the money AND near expiry, exactly the profile that makes short-dated at-the-money options feel electric.

Gamma and the hedge that never sits still

For anyone holding options, gamma is the reason a hedge drifts. A desk that sold calls and bought stock to be delta-neutral finds its delta moving the instant the stock does — negative gamma means the hedge is always a step behind, forcing it to buy high and sell low to re-hedge. That constant adjustment, across the market's largest positions, is a real force on the tape near big expirations, part of how market makers make money.

For a retail trader the read is simpler: gamma tells you how stable your delta is. A low-gamma position — deep in the money, or months out — behaves predictably. A high-gamma position — at the money, days to expiry — is twitchy. And gamma never comes free: the contracts with the most of it also carry the fastest time decay, so a buyer paying for explosive potential pays for it every day the move does not come.

FAQ

What is gamma in options in simple terms?

Gamma is how fast an option's delta changes when the stock moves $1. If delta is the option's speed, gamma is its acceleration. High gamma means delta — and the option's value — can change quickly on a small move.

Why is gamma highest at the money?

An at-the-money option is the most uncertain about finishing in or out of the money, so a small stock move changes its odds the most — and delta with it. Deep in- or out-of-the-money options are already near-certain either way, so their delta barely moves and gamma is small.

Why does gamma increase near expiration?

With little time left, an at-the-money option's fate turns on the next small move, so its delta reacts violently — high gamma. Longer-dated options have time to absorb moves, so their delta shifts gently and gamma stays low.

Is high gamma good or bad?

It depends on your side. A buyer likes positive gamma — the position accelerates in their favor on a big move. A seller is short gamma and is hurt by big moves in either direction, the risk they collect premium for.

What is a gamma squeeze?

It is a feedback loop: dealers short a lot of short-dated call options must buy the underlying stock as it rises to stay hedged (negative gamma forces it). That buying can push the stock higher, forcing still more hedging — a squeeze that comes from option positioning rather than fundamentals.