What a GEX Calculator Actually Computes
Every product in this category runs the same arithmetic. Take each contract's gamma, multiply by open interest and the contract multiplier, scale by spot, sign calls positive and puts negative, and sum. That is it. Our GEX formula walkthrough takes the expression apart term by term, and there is nothing proprietary in it.
What separates one calculator from another is the four decisions made around the arithmetic: which chain the open interest came from and how stale it is, how many expirations were included, which unit the output is quoted in, and whether the dealer sign assumption was disclosed or quietly assumed. Two competent builds using identical formulas routinely produce different call walls because they answered those four questions differently. Neither is wrong. But if you cannot find out how a vendor answered them, you are reading a number you cannot audit.
How to Evaluate One
Methodology transparency
Ask whether the vendor states, in public, on its own site, how it calculates the number. Barchart does: its per-ticker gamma exposure pages specify "4 nearby expirations, based on a 1% move of the underlying security using gamma and open interest," sourced from the consolidated OPRA feed. That single sentence tells you more about what you are looking at than a page of marketing. Vendors that describe their levels only as proprietary are asking for trust you have no way to calibrate.
Unit convention
The two standard quotes differ by a factor of spot × 0.01. On SPX near 7,700 that is 77, so the same book quoted per-$1 and per-1% differs seventy-sevenfold, and neither figure is incorrect. Michael Perfiliev's widely copied walkthrough states the conversion explicitly, "Option's Gamma * Contract Size * Open Interest * Spot Price ^ 2 * 0.01", and reports results in billions per 1% move. If a chart shows an unlabelled axis, its magnitude is uninterpretable, and comparing it against a second vendor's figure is meaningless.
Open interest freshness
Open interest settles overnight. A calculator reading a live intraday chain is working from yesterday's settled figures plus whatever the feed reports, and a calculator reading a morning settlement file is working from the same underlying numbers with the staleness made explicit. The failure mode worth knowing about is a chain that returns open interest of zero on every row: gamma times zero is zero, so the pipeline does not error, it produces a confident, well-formed, entirely fictional result. We hit exactly that and documented it, because a GEX pipeline fails silently far more often than it crashes.
Sign-convention honesty
Open interest proves a contract exists. It does not reveal which side of it a dealer holds. Every public-data calculator resolves this by assuming dealers are long calls and short puts. SpotGamma, which sells these levels for a living, says so directly on its free chart page: "This is a standard net gamma curve, using basic assumptions that options liquidity providers are short put options and long calls." Treat the sign as a hypothesis. Where it is wrong, the level was never real. Our gamma exposure primer covers what the profile does and does not imply once built.
Accountability
This is the criterion almost nobody applies, and the reason this list is ordered the way it is: can you check the vendor's levels against anything? Ticker counts, update frequencies and model counts are capability metrics, not accuracy metrics. What makes a claim falsifiable is a published method, a capture time on every number, and any rate reported next to the sample and the condition it was measured under rather than on its own. Across the products below that combination is close to nonexistent, worth pricing into the decision. It is also the standard that made us withdraw our own wall hold rate in August 2026: it was measured on a third-party definition of a wall and was dominated by how far that wall sat from spot, and a rate that cannot survive its own conditioning is not evidence.
The Tools, by the Job You Need Done
All pricing and feature detail below was read from each vendor's own public pages on 20 August 2026. These figures move; re-check before subscribing.
Best for intraday dealer flow and research depth: SpotGamma
SpotGamma lists Essential at $99/mo and Alpha at $299/mo, with annual billing advertised at 50% off the first year for new subscribers. Essential includes HIRO, Equity Hub across 3,500+ stocks, Tape across 3,000+ tickers, TRACE, Key Levels, a volatility dashboard, the Founder's Note and twice-weekly Q&As; Alpha adds the Synthetic OI Lens and TRACE enhancements. HIRO is the genuine differentiator, an intraday view of dealer hedging flow rather than a once-a-day open-interest snapshot, and the breadth of single-name coverage plus the daily written research is not matched anywhere else in this list. If you want a SpotGamma alternative, be clear about which piece you are replacing, because the free tools below replace the levels, not the intraday flow or the research. Our SquawkFlow and SpotGamma comparison works through that split feature by feature.
Best multi-model level set: MenthorQ
MenthorQ prices Premium at $129/month after a $39 first month, and Pro at $349/month after a $174.50 first month, with a stated seven-day money-back guarantee. Premium advertises "20+ Trading models," 10+ integrations and a large academy library; Pro layers on live trading sessions and weekly mentorship. Its key levels centre on SPX, QQQ and VIX, with data spanning stocks, ETFs, indices, crypto and futures. The pitch is breadth of models rather than one canonical gamma number, which suits traders who want several independent level sets to agree before acting.
Best GEX bundled with options flow: Unusual Whales
Unusual Whales runs Retail Basic at $50/mo, Retail Pro at $75/mo and Retail Max at $120/mo. Basic and Pro include "SPX Market Maker Exposure (10-min updates)"; Max upgrades that to "1-minute SPX Market Maker Exposure." A GEX heatmap covering all US tickers is included at every tier. If you already want the flow product, the exposure view arrives with it, which makes the marginal cost of the gamma data effectively zero.
Best dedicated GEX dashboard at the low end: GEXBoard
GEXBoard prices Starter at $19/mo, Pro at $39/mo and Trader at $79/mo during a beta that the page says ends 1 October, with regular rates of $39, $79 and $149. Starter covers ten tickers and weekly plus monthly expirations; Pro extends to thirty tickers including SPX and all DTE modes with a heatmap and wall migration; Trader adds DEX, vanna and charm profiles plus a 30-day GEX history. The page states that "GEX levels recalculate continuously throughout the trading day using real-time options chain data and live spot prices," and also that "We don't offer free trials."
Best free per-ticker screen: Barchart
Barchart's gamma exposure pages are viewable without an account, cover indices, stocks and ETFs, and state their method openly, as noted above. The page says gamma exposure "is calculated and updated throughout the day." For scanning where gamma sits on an arbitrary single name, this is the fastest free answer available, and the disclosed methodology means you know what you are comparing.
Best free daily SPX curve: SpotGamma's free chart
SpotGamma publishes an SPX gamma exposure chart at no cost, stating that it "is updated daily using current options positioning data" and that "These curves are a small fraction of what SpotGamma monitors." No account appears necessary for the chart itself. It is a daily shape, not an intraday tool, and the vendor labels it as such.
Best DIY build: Perfiliev's walkthrough
Perfiliev's guide is free and reproducible end to end: pull the Cboe delayed-quotes options chain as a CSV, pivot strike against total gamma in Excel, then move to Python for the full gamma profile. Building it once is the cheapest way to learn which assumptions every commercial dashboard is making on your behalf, and the cost is an afternoon.
Best free, no-signup SPX levels with a published method: SquawkFlow (that's us)
Our SPX gamma exposure page needs no account and is free. The walls come from a full-chain snapshot built each morning before the open: Cboe settlement open interest across roughly 21,000 listed SPX contracts, crossed with Schwab implied volatility. Because the input is settled open interest, the walls are fixed for the session by construction, a refresh every 30 minutes repoints spot, the expected range and the 0DTE magnet, not the walls. Two things are unusual here. First, every number ships with the time it was captured and the settlement date its open interest came from, and the overnight change in that open interest is published as a count from our own archive rather than an estimate. There is no wall hold rate: we showed one until August 2026 and withdrew it, because it was measured on a third-party definition of a wall and was dominated by distance. Second, an intraday session log records structural changes as they happen, timestamped rows tagged RELOCATION, FLIP CROSS, REGIME, TEST or QUIET, each with the spot print and a plain description of what the levels did, with no directional call attached. Our method note documents the pipeline including the zero-open-interest bug that once made it serve $0. If you need intraday dealer flow or single-name coverage, the paid products above are the right tools.
How to Shortlist
Work backward from the decision. Intraday SPX positioning wants a genuine intraday flow product, which means SpotGamma's HIRO or Unusual Whales' one-minute exposure view. Single-name gamma across a watchlist wants breadth, so Barchart free or GEXBoard paid. Daily SPX levels you intend to mark on a chart before the open need accuracy over frequency, so read the published method and the capture time before the refresh rate. And if you are still deciding whether gamma belongs in your process, build it once from the Cboe chain and compare your output against two free dashboards; our checklist for reading a free gamma exposure chart is the fastest version of that exercise. Why published dashboards disagree at all is covered in SPX gamma levels.
The Mistakes That Cost the Most
Comparing two vendors' numbers without checking their units is the expensive one, and the factor of 77 makes it look like a data error rather than a convention mismatch. Treating the dealer sign assumption as observed fact is the second, it is a modelling convention that is roughly right for index products and sometimes wrong for single names around events. And the most persistent is confusing update frequency with accuracy. A level recalculated every second from settled open interest is not fresher than the same level computed once at 9am; it is the same number redrawn. What tells you whether it works is a hit rate, which is exactly the statistic almost nobody publishes.
Educational content, not financial advice. See our risk disclosure.