This guide covers everything you need to know about prediction markets: how they work, how people profit, and what you can build on top of them.
Quick Reference
| Term | Meaning |
|---|---|
| YES/NO shares | Tokens that pay $1 if an outcome happens (YES) or doesn't (NO) |
| Split | Converting $1 into 1 YES + 1 NO token |
| Merge | Converting 1 YES + 1 NO back into $1 |
| USDC | Stablecoin (worth $1) used on Polymarket |
What Is a Prediction Market?
A prediction market lets you buy shares that pay $1 if something happens, $0 if it doesn't.
Example: "Will Taylor Swift announce a new album before March 2025?"
- YES shares at 35¢ = market thinks 35% chance she announces
- If she announces: YES pays $1, NO pays $0
- If she doesn't: YES pays $0, NO pays $1
Buy YES at 35¢, she announces, you get $1. That's a 3x return.
The key: You're trading against other people, not a casino. Better information = profit.
Why Prediction Markets Matter
They're accurate. When real money is on the line, people do research. Prediction markets consistently beat polls and expert forecasts.
They cover everything. Politics, economics, crypto, sports, weather, culture. If it can be verified, there's probably a market.
They're open to builders. Unlike sports betting (where winning gets you banned), prediction markets welcome profitable traders and developers.
Polymarket vs Kalshi
| Polymarket | Kalshi | |
|---|---|---|
| Type | Crypto (Polygon blockchain) | US-regulated exchange |
| Currency | USDC | USD |
| Who can use | Global (US restricted) | US only (KYC required) |
| Fees | No trading fees | Trading fees apply |
| Best for | Politics, crypto, global events | Economics, weather |
Bottom line: Non-US users → Polymarket. US users → Kalshi. Builders → both.
How It's Different From Sports Betting
| Sports Betting | Prediction Markets |
|---|---|
| House sets odds with built-in margin | Prices set by supply/demand, no house edge |
| Money locked until game ends | Exit anytime by selling |
| Win too much → account limited | No restrictions for winning |
| Only the book can set odds | Anyone can post orders and make markets |
How Polymarket Works
YES + NO Tokens
Every market has YES and NO tokens. Prices should add up to ~$1 (e.g., YES at 65¢ + NO at 35¢).
Splitting and Merging
Split: Turn $1 into 1 YES + 1 NO token. Happens automatically when a YES buyer matches with a NO buyer.
Merge: Turn 1 YES + 1 NO back into $1. Happens automatically when sellers on both sides match.
Why it matters:
| Holding | Market Prices | Merge Value | Best Move |
|---|---|---|---|
| 1 YES + 1 NO | YES 40¢, NO 55¢ | $1 | Merge (get $1 vs 95¢) |
| 1 YES + 1 NO | YES 55¢, NO 50¢ | $1 | Sell separately ($1.05) |
Resolution
When the event happens: winning tokens redeem for $1, losing tokens become $0.
How to Make Money
1. Information Edge
Know something the market doesn't. Follow niche topics, have domain expertise, do better analysis.
2. Cross-Platform Arbitrage
Buy the cheaper YES on one platform + cheaper NO on another. If total < $1, you profit no matter what.
Example:
| Platform | YES | NO |
|---|---|---|
| Polymarket | 52¢ | 48¢ |
| Kalshi | 45¢ | 53¢ |
Buy Kalshi YES (45¢) + Polymarket NO (48¢) = 93¢ total
| Outcome | Payout | Profit |
|---|---|---|
| YES wins | $1 from Kalshi | 7¢ |
| NO wins | $1 from Polymarket | 7¢ |
7¢ guaranteed profit (7.5% return) regardless of outcome.
3. Copy Trading
Every Polymarket trade is public on-chain. Find consistently profitable wallets, mirror their trades.
Challenge: Speed matters. By the time you see the trade, price may have moved.
4. Market Making
Post buy orders at 49¢ and sell orders at 51¢. If both fill, you earn the 2¢ spread.
Risk: Sharp price moves can leave you holding a losing position.
Airdrop Farming
New platforms often reward early users with token airdrops.
Polymarket: Has a rewards program based on trading activity. Trade markets you're interested in; don't force volume just for points.
Opinion: Newer platform worth watching. Early adopters typically get the best rewards.
Important: No guarantees. If you're losing money just to farm, stop.
What You Can Build
- Arbitrage bot - Monitor prices across platforms, auto-execute when spreads appear
- Copy trading system - Track profitable wallets, mirror their trades
- Wallet leaderboard - Rank traders by PnL, win rate, ROI
- Portfolio tracker - Show positions and performance across markets
- Alert system - Notifications for price moves, whale trades
The Building Challenge
Polymarket is complex: 5+ smart contracts, multiple identifier types, split/merge mechanics. A "buy" might show up as a split + sell on-chain.
Cross-platform is harder: Different APIs, naming conventions, no built-in market matching.
Execution is tricky: Wallet management, transaction signing, gas fees, failed transactions.
Tools That Help
Predexon Data API:
- Complete trade history across Polymarket and Kalshi
- Wallet PnL and performance metrics
- Market matching across platforms (99%+ coverage)
- Real-time WebSocket (faster than native Polymarket)
- Tick-level orderbook history, downloadable as Parquet
Check docs.predexon.com for documentation.
Getting Started
Week 1: Learn the Mechanics
- Create accounts on Polymarket and/or Kalshi
- Deposit $50-100
- Make small trades ($5-10) to understand orderbooks, limit orders, slippage
Week 2-4: Find Your Focus
- Trading: Pick 2-3 categories you know, track prices and news, log your trades
- Building: Start simple (price tracker, alert bot), use Predexon API
- Arbitrage: Compare prices manually first, understand patterns before automating
Scaling Up
- Increase position sizes gradually
- Never risk >10% of capital on one market
- Keep records, review performance
Mistakes to Avoid
- Ignoring orderbook depth - Check liquidity before large orders
- Missing resolution rules - Read how markets settle before trading
- Overconcentrating - Even 90% favorites lose 10% of the time
- Chasing moves - If you don't know why you're buying, don't
- Ignoring time value - Holding at 95¢ for 6 months is only ~10% annualized
Resources
- Polymarket - Leading crypto prediction market
- Kalshi - US-regulated alternative
- Predexon Docs - Data API, WebSocket, tick history
Happy trading.