9to5.edu — prediction markets, sportsbooks, and how to read the Line Shopper

A prediction market lets you buy and sell contracts on the outcome of a future event — a game, an election, an economic number. Each contract is worth $1 if the outcome happens and $0 if it doesn't. The price, in cents, is the market's live estimate of the odds.

A contract trading at 49¢ means the market thinks the outcome has about a 49% chance. The YES side and the NO side always add up to roughly $1: if YES is 49¢, NO is about 51¢. That's the whole pricing model — no American-odds math required (though the Line Shopper can show that format too).

You pay the current price for a contract. If you're right it settles at $1.00 and your profit is the difference; if you're wrong it settles at $0 and you lose what you paid.

A 60¢ contract is not “free money” — a 60% market still loses 40% of the time. You make money by buying contracts that are mispriced, not by picking favorites.

This is the big difference from a sportsbook. There's no bookmaker setting a line and taking the other side — you buy from, and sell to, other traders on an exchange, and the platform just matches orders and takes a small fee. Because anyone can take either side, you can also sell your contract back any time before the event settles, to lock in a gain or cut a loss — as long as someone's there to trade with.

Kalshi is a U.S. exchange regulated by the CFTC — the federal commodity-futures regulator — so it's legally a derivatives market, not a casino. (The state-versus-federal question over sports event contracts is being actively litigated, but the exchange itself runs under federal oversight.) Polymarket is a decentralized, on-chain market; its global site is closed to U.S. persons, with a separate CFTC-regulated Polymarket US for U.S. access.

When the event ends, the market resolves against a defined source: Kalshi settles by published rules tied to official data; Polymarket settles through an on-chain oracle with a dispute window. Payout isn't always instant — it can lag the event by a few hours.

See live prediction-market prices.Open the Line Shopper →

If you already bet on DraftKings or FanDuel, prediction markets aren't a different game — they're the same bets with a different, usually cheaper, structure. Here's what changes.

A standard −110/−110 sportsbook market holds about 4.5%: the house's cut, baked into the price, win or lose. On an exchange there's no built-in margin — YES and NO add up to ~$1 plus a penny or two of spread, and you pay an explicit fee that's usually under ~1% effective. Across a sample of NBA/NHL/MLB markets the measured Kalshi take came in around 0.85% versus ~4.6% at sportsbooks. Same edge, a fraction of the vig — and that gap compounds over a season.

Sportsbooks cut or ban bettors who win. An exchange can't — there's no house to protect. The constraint moves from “the book limits me” to “is there enough volume to get my size down?” Liquid primetime markets are deep; obscure ones are thin, and a big order can walk the book.

The bet types you know all map to a binary question:

• Moneyline — Team A to win  →  YES on “Team A wins.”
• Spread — Team A −3.5  →  YES on “Team A wins by 4+.”
• Total — Over 8.5  →  YES on “8.5+ combined.”

Pick the contract; the price in cents is the implied probability. (The Line Shopper currently shows Moneyline and Totals; spreads are captured but not yet displayed.)

A sportsbook bet is locked once placed — cash-out, where offered, is the book's price, shaved. On an exchange you can sell your position any time there's a buyer: bank a winner early, hedge, or cut a loser at the live price.

Because the same outcome is priced at six venues at once, buying the best price is line shopping — and the price you got versus where the market closes (its closing line value, or CLV) is the cleanest measure of whether you're beating the market over time. The devigged sportsbook price is a useful fair-value reference; comparing it to the Kalshi or Polymarket price shows where the value is. The Line Shopper exists to make that comparison instant.

Prediction-market prices aren't always sharper. Liquid markets can beat a sharp sportsbook; thin ones just aggregate a small, often-retail crowd and move slowly. Read the liquidity before you trust the price.

Compare prices for yourself.Open the Line Shopper →

Every price on the Line Shopper is shown in cents. Cents are the native unit of prediction-market pricing: 49¢ means the market thinks the outcome has roughly a 49% chance of happening.

You pay 49 cents for a contract; if the outcome happens, you receive 100 cents and your profit is 51 cents. The toggle in the top right switches the display to American odds — the +/- format sportsbook bettors see. Same probabilities, different presentation: 49¢ is about +104 in American; 60¢ is about −150.

Each game has one or two markets — Moneyline (who wins) and, where Kalshi offers it, Totals (over or under the combined score). Every outcome gets its own row: the home team's price, draw if applicable, the away team's price. For Totals, the row is the Over side; the Under is the implied complement.

Six columns: Kalshi and Polymarket on the prediction-market side; DraftKings, FanDuel, BetMGM, and Caesars on the sportsbook side. Each cell is that venue's current price for that outcome.

The lowest cents in each row is shaded green — that's the cheapest place to buy that contract, all else equal, which is the whole point of line shopping. The highlight is plain arithmetic: lowest number wins. It is not a recommendation to bet on that outcome.

We pull fresh prices about every ten minutes — the “updated N min ago” label on each board tells you exactly how fresh it is. The actual venue price the moment you click may differ by a cent or two.

Try it now.Open the Line Shopper →

The Line Shopper shows you where the best price is; the actual order happens on the venue's own site. Clicking a price cell opens that market in a new tab. Here's what trips people up the first time — by platform.

• Fund with ACH or wire, not a debit card. Debit carries a ~2% fee; ACH and wire are free. Expect a withdrawal hold the first time — deposits are tradeable immediately, but cashing out waits for the deposit to clear (a few days; longer for a brand-new bank). Fund from the bank you'll withdraw to.
• Use a limit order, not market, when you can. Kalshi's taker fee (on market orders) is largest right around 50¢; the maker fee (when your limit order rests and gets filled) is much smaller, often zero. If the game is hours away, posting a limit a cent or two better than the best ask is usually worth it.
• Settlement isn't instant. Payout comes when the market resolves against its official source — often hours after the final whistle.

• U.S. residents: use Polymarket US, the CFTC-regulated version. Don't VPN into the global site — it detects VPNs and can freeze accounts.
• Fund with USDC on the Polygon network — only Polygon. Sending USDC on Ethereum mainnet (or any other chain) is the most common way new users lose a deposit. Check the network every time.
• Your first trade triggers a one-time approval. It looks like a scam prompt; it isn't — it's a normal one-time token authorization. Keep a few dollars of POL in the wallet for gas.

A market order takes the best price showing and fills now — you pay the taker fee. A limit order names your price and rests on the order book until someone matches it — cheaper (the maker fee), but it might not fill.

• Liquidity. A 47¢ price is only real if there's volume at 47¢. Check the depth; if you're buying more than what's resting there, you'll walk the book and pay more (slippage).
• Fees. Maker versus taker can decide a close trade on Kalshi. Sportsbook prices already include the vig.
• Yourself. Trade because the price is good, not because you want action. If you're past what you set aside to lose, stop — the market is open tomorrow too.

Find a matchup.Open the Line Shopper →