How Prediction Markets Work: A Practical Guide

A prediction market is a market where shares pay out $1 if an event happens and $0 if it does not. During the 2024 US presidential election, Polymarket was trading "Will Donald Trump win the 2024 US presidential election?" at around $0.61 in late October, implying a 61% market probability. By election night, the contract resolved at $1.00 and anyone holding Yes shares collected the full dollar.

That is the entire mechanic. Everything else is detail about how prices form, what it costs to participate, and what can go wrong.

What a Prediction Market Actually Is

Every contract is binary. At resolution, each share is worth exactly $1 (if the event happened) or exactly $0 (if it did not). Between now and resolution, shares trade at whatever price buyers and sellers agree on. That price is a direct probability estimate: $0.62 means the market collectively thinks there is a 62% chance the event resolves Yes.

If shares for "Will X win the election?" trade at $0.62, you have two ways to act on that price. You can buy Yes shares at $0.62, and if the event happens, each share pays $1.00, giving you a $0.38 profit per share. Or you can buy No shares (which trade at roughly $0.38, since Yes + No = $1.00), and if the event does not happen, each No share pays $1.00, giving you a $0.62 profit per share.

You do not have to hold to resolution. If you bought Yes shares at $0.62 and the price moves to $0.78 because new information favors the outcome, you can sell at $0.78 and take the $0.16 per share profit without waiting for the event to settle. This is where prediction markets start to feel like trading rather than gambling: you are making a directional bet on a probability, and you can exit at any time when the market reprices your position.

Resolution works through an oracle, which is a system or entity that reads the outcome from a trusted source (election results, official sports data, government announcements) and triggers settlement on-chain. On Polymarket, UMA Protocol serves as the oracle. When a market closes, the oracle reports the outcome, the smart contract processes it, and winning shares automatically receive $1.00 USDC. The whole settlement process typically takes a few hours to a day depending on when results are officially confirmed.

How Prices Move and Why

Prices move when buyers and sellers disagree about the probability. If a poll drops showing a candidate up ten points, people who read that poll before the market reprices can buy Yes shares at the old (lower) price, pushing the price up as they do. The price movement itself becomes new information for everyone else watching.

This is structurally different from sports betting and casino games. In sports betting, you trade against the bookmaker, who sets lines with a built-in margin (the vig, typically 4-10% depending on the book). In casino games, you trade against the math, meaning the house edge is fixed and publicly defined. Prediction markets are peer-to-peer: you trade against another person who holds the opposite view.

That distinction has one consequence that matters: prediction markets are the only format where positive expected value is consistently achievable if you genuinely know something the market does not. A casino's house edge is fixed by design. A sportsbook's margin is locked in before you bet. A prediction market price reflects the aggregate of all participants' information, and if your information is better or more current, you have a real edge. For a full comparison of expected value across formats, see the EV comparison article.

Prices also move when large orders hit a thin order book. A $5,000 buy order in a market with only $8,000 of liquidity on the ask side will push the price up noticeably. This price impact is not a fee, but it does affect your effective entry price. In liquid markets (Polymarket's top markets often have $1M+ in open interest), impact on individual trades under $1,000 is negligible.

Placing Your First Trade

I opened Polymarket, connected MetaMask, deposited $50 in USDC via Coinbase, and placed my first trade in about 20 minutes. Here is what that process actually involves.

Wallet setup. You need a Web3 wallet on Polygon. MetaMask works fine. You can also use Coinbase Wallet or any EVM-compatible wallet. Polymarket supports social login (Google or email) that creates a wallet automatically if you do not want to manage keys yourself, but that introduces custodial risk.

Getting USDC on Polygon. Polymarket runs on Polygon, and the only accepted collateral is USDC. The friction point for most people is bridging: you need USDC specifically on the Polygon network, not on Ethereum mainnet. The easiest paths are buying USDC directly on Coinbase and withdrawing to Polygon (Coinbase supports native Polygon withdrawals), or using the built-in on-ramp inside Polymarket's deposit flow, which connects to MoonPay or similar fiat-to-crypto services. Polymarket also has a direct card deposit option that handles the bridging automatically, at a higher effective fee.

Finding a market. Markets are listed by category: politics, sports, economics, crypto, culture. Each market page shows the current Yes/No price, total liquidity, the resolution criteria (read this carefully), and the resolution date. The resolution criteria are the most important thing to check before entering any position. Markets have been disputed and resolved against the "obvious" outcome because of how the criteria were written.

Reading the order book. The difference between the best ask (lowest price someone will sell Yes to you) and the best bid (highest price someone will pay to buy Yes from you) is the spread. A market with Yes shares at $0.65 ask and $0.63 bid has a $0.02 spread. That spread is a real cost: if you buy at $0.65 and immediately try to sell, you get $0.63, losing $0.02 per share. In liquid markets, spreads are 1-2 cents. In thin markets, they can be 5-10 cents or more.

Placing the order. You can place a market order (fills immediately at the best available price) or a limit order (fills only at your specified price or better). I default to limit orders set 1-2 cents off the best ask, which usually fills within minutes and avoids paying the full spread.

Selling before resolution vs holding to settlement. If you believe the market has repriced in your favor, selling before resolution locks in gains without waiting. The tradeoff is that if you are right and hold to settlement, you receive the full $1.00 per winning share rather than whatever partial gain a mid-market exit provides.

No KYC is required on Polymarket at the time of writing, though US residents have been blocked in the past and the situation has shifted several times as the regulatory picture around prediction markets evolves. A VPN does not change the on-chain reality, but it does change what the front end serves you.

What It Costs

Polymarket currently charges a 2% fee on profits at settlement, not on every trade. If you buy 100 Yes shares at $0.65 and they settle at $1.00, your gross profit is $35.00, and Polymarket takes $0.70. If you sell before settlement, no platform fee applies; your only cost is the spread.

Gas fees on Polygon are genuinely negligible, around $0.01 per transaction. This is a meaningful improvement over Ethereum mainnet-based markets or any CEX that charges withdrawal fees calculated as a percentage of the transfer.

The real cost structure for a prediction market trade looks like this: half the spread on entry (since the mid-price is your fair value reference), half the spread on exit or the 2% settlement fee if you hold to resolution, plus gas. On a liquid market, a $100 position might cost you $1.00-1.50 total if you hold to settlement. On a thin market, the spread alone could cost you $3-5 to enter and exit.

For comparison, a crypto casino deposit and withdrawal cycle has a similar cost profile. Depositing to BC.Game via Lightning or on a low-fee chain costs a few cents in fees, comparable to Polygon gas costs. The how to deposit via Lightning guide covers the specific fee structure for casino deposits if you want to compare the numbers directly.

Opportunity cost is the hidden expense. A market that resolves in three months ties up your USDC for that period. If your capital could have been earning yield elsewhere (Polygon USDC on Aave was paying 4-8% APY through much of 2024), that foregone interest is a real cost of holding an open position.

Risks Nobody Talks About Enough

Oracle disputes. Polymarket has had contentious resolutions. The most notable was the "Who won the presidential debate?" market in 2024, where the resolution criteria were ambiguous and UMA token holders voted on the outcome. The process worked as designed, but several large traders received what they considered an incorrect resolution. Oracle risk is real, particularly in markets where "who won" is a matter of opinion rather than a clear official result. Before entering any market, read the resolution criteria twice and consider whether there is any realistic scenario where an outcome you consider obvious could be disputed.

Thin liquidity. Most markets on Polymarket outside the top 20 by volume have liquidity measured in tens of thousands of dollars, not millions. Trying to size into a $50,000 open interest market with a $5,000 position will move the price against you on entry and make it difficult to exit without significant impact. I have seen personally that a $2,000 buy order in a thin market moved the price by four cents, which is a $80 cost on a position I was trying to enter at scale.

Adverse selection. This is the risk that gets almost no coverage. The person on the other side of your trade may have material information you do not. Political insiders trading election markets, sports bettors with injury news, traders with access to economic data before public release: prediction markets aggregate information, and if you are the least-informed participant, you will consistently be the one providing value to better-informed traders. This is structurally different from casino games where your counterparty is a fixed mathematical edge, not a potentially better-informed human.

Regulatory risk. Kalshi successfully sued the CFTC in 2024 to offer election markets in the US, which was a meaningful legal development. But the regulatory environment remains unsettled. Several states have signaled they consider some prediction market contracts to be unlicensed gambling. Access from specific jurisdictions can be cut without notice. If Polymarket's front end is blocked in your region, recovering funds from the underlying smart contracts is possible but requires technical familiarity with on-chain interactions.

You do not know who you are trading against. This is the transparency gap that distinguishes prediction markets from provably fair casino games. In a provably fair crash game, you know exactly the house edge: it is published, verifiable from the formula, and does not change based on who you are. In a prediction market, your counterparty is anonymous and may be far better informed than you. The information asymmetry is structural and unavoidable. Tools like the compare tool can help you think through when the transparency of a known house edge beats the uncertainty of a peer market.

For a deeper treatment of the profitability question, including how to estimate whether you actually have edge in a given market, see can you make money on prediction markets.

FAQ

Do I need to verify my identity to use Polymarket?

No. Polymarket does not require KYC. You connect a wallet and trade. US residents have faced access restrictions at various points, which is a separate question from identity verification.

What happens if the oracle reports the wrong outcome?

UMA Protocol has a dispute mechanism. If someone believes the reported outcome is incorrect, they can file a dispute by staking UMA tokens. Token holders vote on the correct resolution. This process has worked correctly in most cases, but it introduces delay and does not guarantee the outcome you expect.

Can prediction market prices predict outcomes better than polls?

The historical record is mixed. Prediction markets outperformed polling aggregates during the 2016 and 2024 US presidential elections. They performed worse than polls on some Brexit and European election outcomes. Markets are as good as the information participants bring, and they can be distorted by large traders with non-information-based reasons to hold positions.

What is the minimum trade size?

There is no formal minimum on Polymarket. Gas costs on Polygon are low enough that $5-10 positions are economically viable, though the spread will eat a disproportionate share of any potential profit on small positions.

Is prediction market income taxable?

In most jurisdictions, yes. Profits from prediction markets are generally treated as capital gains or gambling income depending on your jurisdiction. In the US, there is no settled guidance distinguishing prediction market profits from either category. The crypto gambling taxes guide covers the general framework, though you should consult a tax professional for specific advice.

How is Polymarket different from sports betting sites?

The core mechanical difference is peer-to-peer trading versus trading against a bookmaker. On a sports betting site, the operator sets the line and takes the other side of your bet, with a built-in margin. On Polymarket, you trade against another user at a price set by supply and demand. The bookmaker model means you always pay the vig. The prediction market model means you might face a better-informed counterparty, but if you have an edge, the payoff is not capped by a margin.

The EV comparison article covers the expected value math across prediction markets, sports betting, and casino games with specific numbers. If you want to model the actual house edge across formats, the house edge calculator lets you input your specific bet parameters.

Last updated: March 2026. Polymarket interface and fee structure may change. Verify current terms on their site.