No Vig Isnt No Edge: Prediction Markets vs Sportsbooks
Two bettors, one game. One takes $100 on Cavaliers +3.5 at -110, the other takes $100 on Pistons -3.5 at -110, and the sportsbook keeps $9.09 whoever covers. Sports Illustrated's Geoff Ulrich calls that the vig. Prediction markets say they've done away with it: no house, only traders, and Yes plus No adds up to $1.00.
I spent 15 years grading lines for a Vegas book, and that job taught me one rule. When someone says there's no house, find out who is pricing the bet against you. On Kalshi or Polymarket, somebody still is. They just don't wear the uniform anymore.
The $9.09 Tell: How a Sportsbook Gets Paid
Start with 52.4%. That's the implied probability of a -110 price (110 ÷ 210), and in a -110/-110 market both sides carry it. Add the two together and, per PredictionHero, you get about 105%.
That extra ~5% is the book's cut. It's built into the price before the opening tip, and you pay it every time you click "place bet."
Ulrich's Sports Illustrated example puts it in dollars. On Cavaliers +3.5 (-110) / Pistons -3.5 (-110), a winning $100 bet profits $90.91. Take $100 on each side and the book pays the winner $90.91 out of the loser's $100. It keeps $9.09. That's a house edge you can see right there on the screen.
Sports Illustrated describes the setup plainly: the sportsbook takes the other side of every wager and profits when its odds favor the house over time. The cash-out button works the same way. MetaMask notes that books price cash-outs aggressively, because the goal is managing their liability, not handing you a fair exit.
The book doesn't need to pick winners. It just needs both sides to pay it.
"No Vig" Isn't "No Edge": Who's Really Across From a Kalshi Contract
An event contract trades between $0.01 and $0.99 and settles at $1 if the outcome happens or $0 if it doesn't (Action Network). PredictionHero notes that Yes and No add up to roughly $1.00 before fees. So the 105% overround is gone. The edge against you is still there. It has moved to three other places.
Fees. Sports Illustrated reports that prediction-market platforms make money from fees on trading volume, whether you win or lose. The margin didn't disappear. It turned into a separate charge.
Market makers. Action Network explains that market makers post buy and sell orders on both sides to keep the market liquid. That's a real service. But they are professionals who price contracts for a living, and their spread is their paycheck. They are the house without the logo.
Thin liquidity. The YouTube explainer Prediction Markets vs Sportsbooks: The Difference Most Bettors Miss warns that these markets aren't an oracle: thin markets, hype, bad incentives and low liquidity can all produce bad prices. It offers two questions to ask before every trade. Who set this price? Who am I trading against?
The money is real and growing fast. DeucesCracked reports that DraftKings' annualized prediction-market volume went from $2.3 billion to $11 billion within months. More volume pulls more sharp money into those order books. Sharp money makes prices more efficient, which leaves a weekend bettor less room to find an edge.
Then there's the legal ground under your bankroll:
- April 2026: the Third Circuit sided with Kalshi against New Jersey, finding its sports contracts fall under federal commodities law (Action Network).
- A few months later: a federal court in Utah let the state enforce its gambling laws against Kalshi (Action Network).
- Since late 2025: Kalshi's CFTC-regulated sports contracts have been challenged in court in more than a dozen states, with rulings going both ways (PredictionHero).
A venue that a court could shut down in your state is a risk to your bankroll. No contract price includes it.
One Formula, Every Venue: Turn Any Price Into Implied Probability
Three conversions let you price any bet at any venue:
- Negative American odds: odds ÷ (odds + 100). So -110 = 110 ÷ 210 = 52.4%.
- Positive American odds: 100 ÷ (odds + 100). So +150 = 100 ÷ 250 = 40%.
- Event contract: the price is the probability. $0.55 = 55%.
Then take the step most bettors skip: add the platform's fee to the contract price before you compare anything. A $0.55 contract with a fee on top costs more than 55%.
Here's a side-by-side. The sportsbook hangs your side at -110, which works out to 52.4%. The exchange lists the same outcome at $0.53, which is 53% before fees and more after them. In that case the book's -110 is already the cheaper price, vig included. Now flip it. At $0.51 you'd have 1.4 cents of room, and the fee decides how much of that survives.
Tech-Insider puts the exchange's typical pricing edge at 1-2 cents. A fee can wipe out 1-2 cents in a single trade, so do the math before you trust it.
Action Network's verdict for bettors who already shop lines is the right one. Once fees and vig are counted, the best number can turn up at either venue. No venue wins every time, so you compare every time. If the conversions still feel slow, these odds calculation hacks will make them second nature.
A price you haven't converted is just a feeling with a decimal point.
What Line Shopping Is Worth Before You Read a Single Injury Report
For about 90% of weekend bettors, line shopping earns more than handicapping. I'd bet my old grading sheets on it.
Here's why. Every half-point or cent you save is a refund on vig you'd have paid anyway. Take a hypothetical: one book hangs your side at -110 (52.4%) and another has it at -105 (51.2%). Taking -105 lowers your break-even by 1.2 points. You didn't watch film or check the weather to get it. You opened a second app.
That 1.2 points doesn't stay on one ticket. It applies to every bet you place all season. The bettor who settles for -110 by habit gives that margin back every weekend, and nothing on the bet slip ever shows it.
Parlays run the same math in reverse. A parlay is a tax on hope: it stacks the book's margin on every leg, so a two-, three- or six-leg ticket pays the vig two, three or six times. A single at the best available number beats a lottery ticket at the worst one.
DraftKings — Bet $5, Get $200 in Bonus Bets (code PBDK200) A $5 qualifying bet is the cheapest way to put a second app on your phone and start comparing its number against the -110 you've been settling for. 21+ only, T&Cs apply. Bet Now
Your Move: Open the Second and Third Account
Tech-Insider says licensed sportsbooks lead on the two things a recreational bettor uses most: bet variety and promos, with welcome offers ranging from $150 to $1,500. That's the practical case for adding books to your rotation. Each new account is another price on every game you bet, and the welcome offer is a bonus on top of it.
The bonus comes with one condition. A bonus is only worth its playthrough math, never its headline number. Before you count a $1,500 offer as value, work out how much you have to wager to unlock it, at what minimum odds, and what the vig costs you on all that volume. Sometimes a $150 offer with light playthrough beats a $1,500 one with heavy playthrough.
The move is simple:
- Open accounts at two or three licensed books where you're 21+ and online betting is legal.
- Read each welcome offer's terms and run the playthrough math before you deposit.
- Check every line at every book before you bet, and let the best number decide where the money goes.
Mind the map. Dimers notes that real-money online sportsbooks are banned in states such as Texas and California, and prediction-market legality is still being fought state by state. Bet only where the product is legal for you.
Licensed books don't earn a spot in your rotation for loyalty. They earn it with prices. Three accounts mean three prices on every game, and the best of the three becomes your price.
BetRivers — 2nd Chance Bet up to $500 (code PB500) If your first single at the best number loses, BetRivers gives you a second shot, which makes it a sensible third book for your rotation once you've read the playthrough terms. 21+ only, T&Cs apply. Bet Now
Your Pre-Move Checklist: Run It Before Moving a Weekend Bankroll Anywhere
Before you move a dollar to a new venue, go through all eight:
- Convert every price at every venue to implied probability, using the formulas above.
- Add the real cost: fees on contract prices and the vig on sportsbook lines.
- Ask the two questions: who set this price, and who am I trading against?
- Check liquidity: is there enough money on both sides to fill your order at the price shown?
- Confirm legal status in your state, given the April 2026 Third Circuit ruling, the Utah decision and the challenges in more than a dozen states.
- Run the playthrough math on any bonus before you count it as value.
- Compare at least two licensed books plus the exchange, and take the best real number.
- Size every bet against a set bankroll. Treat it as entertainment money, never income.
Bottom Line
The house never left. It just got harder to spot. At a sportsbook it's the ~5% built into a -110/-110 line. On a prediction market it's in the fees, the market makers' spread and the thin order books. Neither venue beats the house for you. What you control is the price: convert every number, shop every line, play singles over parlays, and run the playthrough math on every bonus. The bettor who does that keeps more of every weekend bankroll than the one chasing the newest app.
21+ only. Gambling involves risk. Bet only what you can afford to lose. If gambling stops being fun, call 1-800-GAMBLER.