Prediction Market Betting Explained: Event Contracts

Prediction market betting is trading event contracts that settle at $1 if an outcome happens and $0 if it does not. The price in cents is the market's implied probability, so a 60 cent contract means the market prices the event at roughly a 60% chance.

Buyers and sellers set that price on an open exchange instead of a bookmaker setting odds and building in a margin. That is what makes platforms like Kalshi and Polymarket different from a sportsbook.

That difference is why bettors are paying attention. A prediction market price carries no bookmaker margin, so it can track closer to true probability than a sportsbook line. It is not free to trade, though: a taker fee and the bid and ask spread sit on top, and they are smaller than a typical sportsbook's vig rather than zero.

Try It: Prediction Market Converter

Every prediction market price maps onto the betting odds you already know. Enter a contract price below to see it as American, decimal, and fractional odds, or enter odds to find the matching contract price. The two panels underneath add each platform's taker fee.

At the default 60 cents the quoted price is −150. Kalshi's taker fee adds 1.68 cents, so the contract really costs 61.68 cents and plays like −161. Polymarket's sports fee adds 1.20 cents, for 61.20 cents and −158. These figures are illustrative, and live fees can change.

Drag the price up and the odds shorten, because a more expensive contract implies a higher probability. The same math powers our standalone Prediction Market Converter, and it is the first step in comparing any prediction market with a sportsbook.

What an Event Contract Is

An event contract is a simple Yes or No claim about a future event, priced between 1 cent and 99 cents. Buy Yes and you are betting the event happens; buy No and you are betting it does not. At settlement the winning side is worth $1.00 and the losing side $0.00.

Here is how to read a contract priced at 60 cents:

• A Yes contract at 60 cents means the market implies a 60% chance the event happens.
• If the event happens, each Yes contract settles at $1.00, a profit of 40 cents per contract before fees.
• If it does not happen, the contract settles at $0.00 and you lose your 60 cents.
• The No side trades near 40 cents, because Yes and No prices add up to about $1.00.

In betting terms, buying Yes at 60 cents is the same as taking −150 American odds (1.67 decimal): you risk 60 to win 40. The price is the probability, which is why a prediction market is often easier to reason about than odds you have to convert first.

Price to Odds at a Glance

The first four columns are the straight conversion. The last two add each platform's taker fee, which is the price you really pay on a market order.

Two rows are worth a second look. A 33 cent contract is +203, not the +200 it is often rounded to. And a 50 cent coin flip stops being even money once the fee lands: it plays like −107 on Kalshi and −105 on Polymarket.

Why the Exchange Model Matters

A sportsbook is the house. It sets both sides of a market and builds in a margin, called the vig or juice. On a typical −110 / −110 market each side implies 52.4%, the two sum to 104.8%, and the book holds about 4.5% of the money wagered no matter who wins.

A prediction market is an exchange where users trade contracts against each other, so supply and demand set the price. Nobody pads the number to protect a margin. The exchange makes its money from a taker fee instead, charged when an order fills against a resting one.

Both Kalshi and Polymarket publish the same fee shape:

$$\text{fee per contract} = r \times p \times (1 - p)$$

Here p is the price in dollars and r is the rate: 0.07 on Kalshi and 0.05 on sports markets on Polymarket's main exchange. The fee peaks at 50 cents and shrinks toward both ends, which is why it matters most on coin flips.

Put both sides of a 50 cent market through that fee and you get a hold you can compare with a sportsbook. Kalshi works out to about 3.4% and Polymarket sports to about 2.4%, against about 4.5% at −110. A resting limit order, called a maker order, pays less or nothing, so patient traders pay less still.

The fee is not the only cost. The bid and ask spread can be a cent or two on a busy market and much wider on a thin one, so the price you can actually fill at matters as much as the headline number. Our Kalshi vs sportsbook breakdown shows where that cost beats a book and where it does not.

Sharp prices, tested

A lower cost is only half the story; the other half is whether the price is accurate. In a study of over 600 million MLB player prop line movements, our sharpest sportsbooks analysis found Kalshi to be one of the sharpest price sources of any book or exchange in the dataset.

Prediction markets are not automatically cheaper or sharper on every event. On liquid markets, though, their prices often behave like a sharp reference line, the same role a no-vig fair odds estimate plays on a sportsbook.

Kalshi vs Polymarket

Two platforms dominate the category, and they are built differently.

Kalshi is a federally regulated exchange and the larger of the two by volume. It is designated by the CFTC and offers sports contracts in most US states, including many where sportsbooks are not legal.

States are contesting that in court, federal appeals courts have split on it, and sports markets are already off in some states, such as Nevada.

Kalshi funds in dollars, charges a 0.07 taker rate, and rounds the fee on an order up to the next cent, which costs small orders proportionally more. Kalshi stopped showing American odds in its app on August 31, 2026, so our Kalshi odds converter does that step for you.

Polymarket is the largest crypto prediction market. Its main exchange runs on the Polygon blockchain, so trades settle on chain and every wallet's positions are public. It charges a 0.05 taker rate on sports, which is 5/7 of Kalshi's fee at every price, and nothing on resting maker orders.

US bettors are routed to Polymarket US, a separate CFTC regulated app with its own fee schedule, so confirm what is available in your state before trading. Convert its prices with our Polymarket odds converter.

Both price the same way, a contract from 1 to 99 cents with the two sides summing to about a dollar, so the skills carry over. The practical differences are fees, regulation, funding, the menu of markets, and liquidity on any given event. Polymarket vs Kalshi compares the two on cost and sharpness in detail.

Finding Value Across Platforms

The reason to convert a prediction market price to odds is to compare it with a sportsbook and see which side offers more than the outcome deserves. The workflow is short:

1. Convert the contract price to odds and add the fee with the converter above, so you compare what you would really pay.
2. Devig the sportsbook line to strip out its margin and recover its fair probability. Our devigging guide explains the math, and the devigging calculator does it for you.
3. Compare the two probabilities. If a contract costs 55 cents after the fee and the devigged sportsbook line says 60%, the contract looks underpriced. If the book's fair line says 50%, the sportsbook's other side may hold the value instead.

On an exchange, a straight devig can mislead when liquidity is lopsided or the spread is wide. Our contributor piece on finding fair value on prediction markets walks through those cases.

When two platforms disagree enough that betting both sides covers every outcome, that is an arbitrage opportunity. The SmartStake Arbitrage Finder scans sportsbooks, exchanges, and prediction markets to surface those crosses. Arbitrage is not risk free: prices move between placements, fees eat thin gaps, and limits get cut, so treat every gap as a candidate.

The same habit of comparing prices across venues is plain line shopping, and the skill underneath it all is judging where the fair price sits. That is the discipline behind positive expected value betting and closing line value. Prediction markets just give you a cleaner starting number.

Futures are where the exchange model changes the most, because you can see both sides of a long dated market and sell before it settles. Read how one contributor uses that in how prediction markets changed futures betting.

Following Sharp Prediction Market Money

The most interesting signal in prediction markets is not the price itself, it is who is trading. Polymarket settles on chain, so every position is public, and some wallets have a long record of pricing sports better than the crowd.

SmartStake Insiders turns that into a feed of Picks from qualified Polymarket wallets. A wallet qualifies only after a daily audit of its full on chain history: at least 200 sports markets traded, a directional return of at least 1% with arbitrage positions excluded, no more than half its markets as arbs, and activity in the last 30 days.

That is the same idea as reading sharp money on sportsbooks, applied to an open ledger. Our Insiders walkthrough shows how to read a Pick and the price it lists. Insiders is part of the Premium plan in the SmartStake app.

Following sharp money is a signal, not a promise. A wallet with a strong record can still be wrong on any single contract, and past performance never guarantees a future result.

The Honest Risks

Prediction markets are cleaner than sportsbooks in some ways, but they are not free money.

• Liquidity varies. A thin market can move a lot on a single order, and you may not fill your whole size at the price you see.
• Fees still apply. Taker fees are largest near 50 cents, and on a tight edge they can be the difference between a good bet and a bad one.
• Regulation is evolving. What is available depends on your state and platform, and the rules and court rulings are still changing.
• The market can be wrong. A price is a consensus estimate, not a fact. Prediction markets have misjudged plenty of events, and any individual contract can lose.

Treat prediction market betting the way you would any other edge play. Use a written bankroll management plan, size your positions, and never stake money you cannot afford to lose.

Frequently Asked Questions

What is prediction market betting? Prediction market betting is trading event contracts that settle at $1 if an outcome happens and $0 if it does not. The price in cents equals the market's implied probability, so a contract at 60 cents means the market prices the event at roughly a 60% chance. You look for value by buying contracts you think are underpriced and holding or selling them before settlement.

How is a prediction market different from a sportsbook? A prediction market is an exchange where users trade contracts against each other, so supply and demand set the price rather than a bookmaker. A sportsbook builds a margin, called the vig, into both sides of its odds. A prediction market has no bookmaker margin, but it charges a taker fee and has a bid and ask spread, so its cost is lower than a typical sportsbook's vig rather than zero.

Do Kalshi and Polymarket charge fees? Kalshi and Polymarket both charge a taker fee of rate x price x (1 minus price) per contract. Kalshi's published rate is 0.07 and Polymarket's sports rate is 0.05, so a 50 cent contract costs 1.75 cents on Kalshi and 1.25 cents on Polymarket. Both sides of a coin flip paying that fee work out to a hold of about 3.4% on Kalshi and 2.4% on Polymarket, against about 4.5% on a −110 sportsbook line. Resting maker orders pay less or nothing.

Are Kalshi and Polymarket odds better than sportsbook odds? Prediction market prices often track closer to true probability than sportsbook odds, and a SmartStake study of MLB player props found Kalshi to be one of the sharpest sources of all. That does not make them cheaper on every event, so convert the price to odds, add the taker fee, and compare it with a devigged sportsbook line before deciding where the value is.

How do I convert a prediction market price to betting odds? Divide 100 by the contract price in cents to get decimal odds, then convert to American or fractional from there. A 60 cent contract is 100 divided by 60, or 1.67 decimal odds, which is −150 in American odds. After Kalshi's taker fee the same contract costs 61.68 cents and plays like −161. The SmartStake Prediction Market Converter does both steps instantly.

Is prediction market betting legal in the United States? Kalshi is an exchange regulated by the Commodity Futures Trading Commission (CFTC) and offers sports contracts in most US states, though states are contesting that in court and sports markets are off in some, such as Nevada. Polymarket serves US bettors through a separate CFTC regulated app, Polymarket US. Check each platform's own signup and location check for your state before you trade. This is general information, not legal advice.

Start Comparing Prices

Prediction markets give you something a sportsbook never will: a price that is the probability, set by an open exchange instead of a house protecting its margin. Convert a contract to odds, add the fee, devig the book on the other side, and you can see where the value sits.

Try the Prediction Market Converter, then explore qualified on chain wallets in the SmartStake app.