Prefer numbers to explanations? See what 309,533 paired price observations say about how closely the two venues actually agree.
Event-contract guides
The math behind prediction-market trading, explained without hand-waving: expected value, fees, cross-platform price gaps, and devigging sportsbook odds into fair probabilities.
What +EV Actually Means on Prediction Markets
+EV (positive expected value) means a contract costs less than its fair probability of paying out. How to compute EV on Kalshi event contracts, with a worked example including fees.
Kalshi Fees, Explained With Actual Numbers
Kalshi's trading fee is 0.07 × price × (1−price) per contract, rounded up. What that costs at different prices, why 50c contracts are taxed hardest, and how to compute your true breakeven.
Same Game, Two Prices: Kalshi vs Polymarket
The same NFL game often trades points apart on Kalshi vs Polymarket. Why the gap exists, when it's a real arbitrage, and the phantom-spread traps that make fake edges look real.
How to Devig Sportsbook Odds, By Hand
Sportsbook odds overstate every outcome's probability by the vig. The multiplicative devig method step-by-step: American odds → implied probability → fair probability, with a worked NFL example.
Is Kalshi–Polymarket arbitrage actually profitable?
The same contract often trades at different prices on Kalshi and Polymarket. We recorded the gap every five minutes across dozens of games and checked what survives the spread and the fee. Our own measurements, including the ones that go against us.
Educational content and impersonal analytics — not investment, betting, or financial advice.