GEX
Call Wall, Put Wall, and Gamma Flip Explained
Options traders often hear about call walls, put walls, and the gamma flip, but the underlying mechanics can be opaque. This guide breaks down each concept, explains how dealer gamma exposure shapes market dynamics, and shows how to read the data that powers these signals. By the end you will understand the definitions, the hedging logic, and the practical steps to incorporate walls and flip levels into your trading workflow.
Definitions
Call wall, put wall, gamma flip, and net_gex_bn are core metrics that describe dealer gamma exposure. A call wall is the strike level that carries the largest positive call gamma exposure. A put wall is the strike with the largest put gamma exposure. The gamma flip is the price at which the dealers’ net gamma changes sign, as shown in the flip column. Net_gex_bn represents dealer net gamma expressed in billions of dollars per one‑percent move; a positive value indicates dealers are long gamma, a negative value indicates they are short gamma.How Dealers Hedge
FinzData assumes dealers are long calls and short puts (customers tend to sell calls and buy puts), and every row states that convention. The net gamma of that portfolio determines how the dealer’s hedging costs respond to price moves. When net gamma is positive, dealers are long gamma: to stay hedged they sell into rallies and buy into dips, which tends to damp moves. When net gamma is negative, dealers are short gamma: they buy as the market rises and sell as it falls, which can amplify moves. Dealers also adjust delta exposure to maintain a neutral position, but gamma drives the dynamic response to larger moves.How Traders Use Walls and Flip
The call and put walls identify the strike levels where dealer gamma exposure is concentrated. Traders watch these levels as potential support or resistance. The gamma flip marks the price where the dealer’s net gamma changes sign; it is a useful regime filter. A move that crosses the flip can signal a shift from short‑gamma to long‑gamma or vice versa. Traders do not use walls or flip as directional signals, but they are valuable for setting risk limits, sizing positions, and timing entries or exits. Each row is stamped 17:00 New York on its session date, so a backtest only sees what was known that evening. In practice, many traders combine wall levels with volatility bands or moving averages to refine entry points.Python example
import finzdata as yf
g = yf.gex("SPY", start="2015-01-01")
print(g[['date', 'spot', 'net_gex_bn', 'flip', 'call_wall', 'put_wall']])
# Compute distance of spot to call_wall and put_wall in percent
# and the share of days spot closed above flip
spot = g['spot']
call_dist = (spot - g['call_wall']) / g['call_wall'] * 100
put_dist = (spot - g['put_wall']) / g['put_wall'] * 100
above_flip = (spot > g['flip']).mean() * 100
print("Call wall distance (%):", call_dist.mean())
print("Put wall distance (%):", put_dist.mean())
print("Share of days above flip (%):", above_flip)Historical Context and Statistics
The GEX data set covers 11,209 tickers, including major indices such as SPX, NDX, RUT, VIX, XSP, and DJX, from January 2010 to the present. Over 4,221 trading sessions have been recorded through October 2026. Analysis of SPX GEX shows that the next‑day volatility is 24.5% annualised after a short‑gamma close compared with 13.5% after a long‑gamma close. Of the 88 sessions with moves over 3%, 72 followed a short‑gamma close. Short gamma predicted the size of moves, not their direction, and past behaviour is not a forecast. These statistics are drawn from the GEX data set and are available for download through the FinzData API.Pricing and Access
The GEX data for a single ticker is available for $19 for five years or $49 for the full history since 2010. GEX Complete, which includes every ticker, costs $295 or $195 as an add‑on. A free FinzData key includes the last 30 days of daily GEX for every ticker, plus the last 12 months of daily US stock bars, COT and SEC fundamentals. The free API key can be obtained at https://api.finzdata.com/.Start free
Begin exploring GEX data with a free API key from https://api.finzdata.com/. For additional data and services, visit the shop at /shop.Frequently asked questions
What is a call wall?
A call wall is the strike level that carries the largest positive call gamma exposure.
What is a put wall?
A put wall is the strike level that carries the largest put gamma exposure.
What does the gamma flip indicate?
The gamma flip is the price where the dealer’s net gamma changes sign.
How can I access GEX data?
Use the FinzData API with a free key from https://api.finzdata.com/ or buy the history you need in the shop.
What is the difference between GEX Complete and single‑ticker GEX?
GEX Complete includes data for all 11,209 tickers, while single‑ticker GEX provides data for one ticker only.
How often is the data updated?
Each row is stamped 17:00 New York on its session date, and new sessions are added each weekday night.