Cross-Venue Arbitrage, Measured: August 12 – September 11, 2026
Every number below is measured by our scanner from live order books and published lines over 29 days (August 12 – September 11, 2026), net of every venue fee at sizes the books could actually fill. No estimates, no extrapolation — this is the archive, summarized.
The headline numbers
- 4,096 distinct opportunity windows opened across 1,818 markets — about 141 per day. (A window is a run of detections on one market with no 30-minute silence; while these stayed open our engine logged 301,273 individual detections, one per price tick.)
- 269,237 of those detections came from prediction-market pairs (Kalshi ↔ Polymarket); 32,036 from sportsbook ↔ prediction-market lines.
- We tracked 2,736 confirmed cross-venue market pairs in this window.
- Average sportsbook overround (vig) across the 20 books we scan: 5.07% per two-way market — the baseline cost any cross-book price has to beat. Live per-book numbers: venue comparison.
How big do opportunities get?
Distribution of net edge across every logged detection:
| Net edge (after all fees) | Value |
|---|---|
| Median | 0.74% |
| Average | 3.48% |
| 90th percentile | 1.87% |
| Largest observed | 842.72% |
The distribution is heavily right-skewed: most opportunities are small, and the occasional large one appears when a single venue's price moves fast on news and the others lag by minutes.
The biggest opportunity of the window
SSG Landers vs Samsung Lions Samsung Lions — a 842.72% net edge detected on August 19 at 13:17 UTC, with $30,383 of measured room at a $3,605 reference stake before the books converged.
How long do they last?
Of the 254,269 detections our engine re-checked 60 seconds later, 100% still cleared all fees — the rest had already been taken or moved.
Speed is the whole game: an opportunity is a live quote, not a standing offer.
Where to look next
- Sportsbook vig, measured and ranked — every book's overround by sport and market, updated every scan
- Kalshi vs Polymarket, market by market — each shared question with both venues' price history
- Arbitrage by sport — which books disagree on MLB, NFL, NBA, NHL and MLS
- Calculators — vig, dutching, no-vig odds, odds conversion and the exact Kalshi and Polymarket fee formulas
Methodology
Our scanner watches Kalshi and Polymarket order books continuously and 20+ sportsbook lines every 15 minutes (pre-game only). For every candidate pair it walks both books level by level to a fillable size, subtracts every venue fee from the published schedules, and records a detection only when the net figure is positive. Each detection is re-checked seconds later and the result stored — including the ones that vanished. The raw per-market history behind these numbers is browsable on every market page.
FAQ
Can I still act on these? These are historical measurements — each one was a live quote that has since converged. The dashboard shows current ones.
Why do opportunities exist at all? Venues price independently and their customers differ. Arbitrageurs closing these differences are the mechanism that keeps venues aligned — see how it works.
Is this a promise of returns? No. It is a record of observed pricing. Execution, fills, fees, account limits, and settlement risk are all yours.
ArbMonster is a data service. Nothing here is financial or betting advice; markets carry risk, venues have age and jurisdiction restrictions, and you are responsible for verifying everything before acting.