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How it works

The questions everyone asks, answered straight.

What is arbitrage?

Two venues sometimes price the exact same outcome differently. When the prices disagree enough, you can back both sides — one on each venue — for less than the fixed payout, so the same amount comes back whichever way the event goes. That difference is arbitrage: profit from a pricing disagreement, not from predicting the outcome.

Example: a prediction-market contract pays $1 if an event happens. YES costs $0.55 on one venue and NO costs $0.42 on another. Buying both costs $0.97; exactly one of them pays $1 at resolution. The $0.03 doesn't depend on the result — only on both orders filling and both markets truly settling the same way.

How do people take advantage of it?

Fund accounts on both venues, then act fast when an opportunity appears: place both orders at (or better than) the shown prices. The card in ArbMonster is literally the order list — which side, which venue, what average price, what size. An opportunity is also repeatable: as long as both order books still have size at the quoted prices, you can keep filling it — the card's “opportunity capacity” shows about how much total the books absorb before prices converge. Every fill narrows the pricing gap; arbitrageurs are the mechanism that keeps venues quoting the same price, and the gap is the market paying for that service.

Why doesn't everyone do this?

Because finding real opportunities is the hard part. Quoted prices lie about size, venue fees quietly eat 1–7% of a trade, they close in minutes, and checking thousands of market pairs across venues by hand is impossible. Most “free money” screenshots you see online are gross numbers before fees, at sizes the books could never fill.

Where ArbMonster comes in

ArbMonster watches every major US sportsbook (25+) plus Kalshi and Polymarket around the clock. It pairs markets that ask the exact same question, walks each order book level by level to a fillable size, subtracts every venue fee, and only shows a card when money is actually left over. Millions of price calculations a day, so you look at conclusions instead of spreadsheets.

Three engines, one dashboard: sportsbook ↔ sportsbook, sportsbook ↔ prediction market, and Kalshi ↔ Polymarket. To our knowledge, no other scanner runs all three cross-venue comparisons in one place.

Reading a card

Potential profit $
Dollars left after buying both sides and paying all fees, at your max stake (set it in the sidebar — cards scale to it).
Net edge %
The profit as a percentage of total money in, after fees. Green up to 2%, light green above. Very large edges are usually short-lived.
found Xm ago
Age of the detection. The older it is, the more likely it's gone — treat every card as a live quote, not a guarantee.
depth: full / partial / unknown
Whether the books can absorb the whole size. “Unknown” means a sportsbook's available size isn't visible, so we cap conservatively.
AI-matched · NN%
How the pair was verified as the same question, with the reviewer's confidence. Always read both markets' rules yourself — settlement differences in edge cases are your risk.
Visual comparison
Both venues' price history with the opportunity window shaded — see exactly when it opened and when it closed.

How fresh is the data?

Prediction-market prices stream in live and the dashboard updates every few seconds. Sportsbook lines refresh every 15 minutes — the header shows a countdown to the next refresh — and only pre-game lines are scanned, because in-play quotes go stale in seconds and would mislead. Live in-game scanning is on the roadmap as we scale, and Pro subscribers will get it first.

What ArbMonster is not

A research and educational data tool, nothing more. It never places trades, never touches your venue accounts, never gives betting or financial advice, and doesn't endorse any venue or activity. It measures public prices and shows the math; what you do with it is entirely your decision.