Event-contract guide
What +EV Actually Means on Prediction Markets
Sports bettors have used 'plus-EV' for years; on event contracts the same idea applies almost literally, because a Kalshi contract pays exactly $1 if you're right. Here's the math, a worked example, and the traps.
1. EV is price vs probability
A YES contract pays $1 when the event happens. If the true probability is P and you pay C dollars, your expected value per contract is P − C. Buy a 58-cent contract on a 62% event and you expect +4 cents per contract before fees. Buy the same contract on a 55% event and you expect −3 cents. The entire game is knowing whether P is really above C.
2. 'True probability' is the hard part — benchmarks beat vibes
Nobody hands you P. The practical benchmark for sports is the sharp sportsbooks' consensus: books like Pinnacle survive by quoting lines sharp bettors can't beat, so their de-vigged price is the best cheap estimate of true probability available to the public. (De-vigging removes the book's built-in margin — see our devigging guide.)
3. Fees move the breakeven
Kalshi charges a trading fee of roughly 0.07 × price × (1 − price) per contract taken. At 58 cents the raw formula gives 1.7 cents, which rounds up to 2 cents — so your effective cost is 60c, and the event needs to be more likely than 60% (not 58%) before the trade is +EV. Thin edges die in fees; always compare fair probability to cost including fees.
4. A worked example
Sharp consensus devigs to 62.0% for a team. Kalshi asks 58c for that team's YES. The fee is 0.07×0.58×0.42 = 1.7c, rounded up to 2c, so effective cost = 0.60. Edge = 0.620 − 0.600 = +2.0 points, or about +3.3% expected return on cost. That's a real (small) edge — the kind that only matters if you can find it repeatedly.
5. Why +EV spots exist at all
Event-contract crowds skew retail and react slower than sportsbook lines, especially early in the week and for less-followed games. Prices also drift on platform-specific flows (one big order moves a thin book). The gap usually closes as game time approaches — being early matters more than being clever.
6. What +EV is not
It's not a guarantee — a 62% event still misses 38% of the time. It's a long-run statement: if your fair probabilities are honest, buying below them profits over many independent trades. Track your closing-line performance (did the price move toward you?) rather than short-run wins to know whether your process works.
See the numbers live
Polykal runs this exact math continuously — de-vigged sharp consensus vs Kalshi prices for every NFL and CFB game, plus cross-platform spread alerts via Discord + webhooks.
Create an account →Free while paid alerts are still closed. Paste any Kalshi or Polymarket link and we'll find its counterpart and what the gap clears after costs, and keep a watchlist of the markets you care about.
Frequently asked
Is +EV betting the same as arbitrage?
No. Arbitrage locks a profit by taking both sides across venues at a combined cost under $1 — riskless but rare and fast-closing. +EV takes one side at a favorable price — it carries variance, but opportunities are far more common. Most profitable event-contract traders live on +EV, not arbs.
Can I compute this myself?
Yes — pull two or three sharp books' moneylines, devig each pair, take the median, and compare against the Kalshi ask plus fees. It's ten minutes per game by hand. Polykal's screener does exactly this computation continuously across every NFL and college football game and shows the edge net of fees — same math, no spreadsheet.
Does this constitute betting advice?
No. Everything here (and in Polykal) is impersonal market analytics computed from public prices — an explanation of arithmetic, not a recommendation to buy any particular contract. Whether any trade makes sense for you is your call.
Impersonal market analytics and education computed from public prices. Nothing on this page is investment, betting, legal, or financial advice, or a recommendation to buy any contract. Polykal is not affiliated with Kalshi, Polymarket, or any sportsbook.