The Complete Guide to
Polymarket Spread Arbitrage
How traders find pricing inefficiencies in prediction markets and capture risk-free (or low-risk) profits. This guide covers everything from basic spread mechanics to advanced execution strategies.
What Are Polymarket Spreads?
On Polymarket, every prediction market has two sides: YES and NO. In a perfectly efficient market, the best ask prices for YES and NO should sum to exactly $1.00 (100 cents). When they don't, a spread exists.
For example, if the best ask for YES is 52.0¢ and the best ask for NO is 51.5¢, the total cost to buy both sides is 103.5¢.
Wait — you just paid $1.035 for a pair of contracts that will settle at exactly $1.00. That's not an arbitrage. That's a negative spread (an overround).
But sometimes the opposite happens. If the best ask for YES is 48.0¢ and the best ask for NO is 49.0¢, the total is 97.0¢ — that's a 3% positive spread. Buy both sides for $0.97 and you're guaranteed a $1.00 payout. That's real arbitrage.
Why Do Spreads Exist?
Polymarket is a decentralized prediction market built on the Polygon blockchain. Unlike centralized exchanges with professional market makers ensuring tight spreads, Polymarket's orderbook can have pricing inefficiencies for several reasons:
Fragmented liquidity
Market makers operate independently on each side (YES/NO). They don't always coordinate, leaving gaps between the best ask prices.
News-driven volatility
When breaking news hits, one side of the market moves faster than the other. This creates temporary mispricings — often lasting seconds to minutes.
Low-attention markets
Not all Polymarket events attract equal attention. Niche markets with lower volume often have wider spreads that persist longer.
Fee structure
Polymarket charges approximately 2% in trading fees. This means only spreads above ~2% represent genuine arbitrage after costs.
The key insight: these spreads are predictable and repeatable. They happen across hundreds of markets, every day. The challenge is spotting them fast enough — which is where automated scanning becomes essential.
How to Spot Arbitrage Opportunities
Finding Polymarket spread arbitrage manually is tedious. You'd need to check the orderbook for every active market, compare YES and NO ask prices, calculate the spread, subtract fees, and assess liquidity — then do it again 60 seconds later.
Here's the systematic approach:
Pull orderbook data via the CLOB API
Polymarket's Central Limit Order Book (CLOB) API exposes real-time best bid/ask prices for every token. You need to query the best ask (sell) price for both the YES and NO tokens of each market.
Calculate the spread
Spread = (YES best ask + NO best ask) - 1.00. If this number is negative, that's the mispricing you can capture. Express it as a percentage: a -0.03 spread means a 3% opportunity.
Subtract estimated fees
Polymarket charges ~2% in total fees across both sides. So a 3% gross spread yields roughly 1% net edge after fees. Only opportunities with positive net edge are worth executing.
Check liquidity depth
A 5% spread means nothing if there's only $10 of liquidity at those prices. Check the orderbook depth to understand how much capital you can deploy at the advertised spread.
Execute both sides simultaneously
Speed matters. Place both the YES and NO orders as close together as possible to minimize the risk of the spread closing before you complete both legs.
This is exactly what Spreadr automates. Our scanner runs this process every 60 seconds across all active Polymarket contracts and alerts you the moment a profitable spread appears.
Real Examples from Live Markets
These aren't hypothetical — they're real spread opportunities detected by our scanner, which currently monitors 476+ markets in real-time.
Will Manchester City finish in the top 4 of the 2026-27 English Premier League season?
Will "Forgotten Island" Opening Weekend Box Office be less than 13m?
Will Xiaomi have the best Chinese AI model at the end of October 2026?
Live data from Spreadr's scanner — updated every 60 seconds.
Want to see more? View the top 5 live opportunities for free →
How Much Can You Make?
Returns from Polymarket spread arbitrage depend on three factors: spread size, liquidity depth, and execution speed.
Even modest edge compounds. If you capture 3-5 opportunities per day at 1-3% net edge with $200-$500 per position, the subscription pays for itself with a single trade.
The real advantage isn't any single trade — it's the consistency. Spreads appear daily across hundreds of markets. Automated detection ensures you never miss an opportunity while manually scanning Polymarket.
Execution & Risk Management
Spread arbitrage on Polymarket is lower-risk than directional trading, but it isn't zero-risk. Here's what to watch for:
Execution risk (leg risk)
If you buy one side and the spread closes before you buy the other, you're left with a directional position. Speed is critical — execute both legs as close together as possible.
Liquidity risk
The advertised best ask might only have $50 behind it. Always check orderbook depth. Spreadr shows liquidity data for every opportunity so you can size accordingly.
Fee drag
Polymarket's ~2% total fee eats into every spread. Only execute when the estimated edge (after fees) is positive. Spreadr calculates this automatically.
Settlement risk
Markets can resolve ambiguously or be voided. Stick to high-volume, well-defined markets to minimize this edge case.
Automating Your Spread Strategy
The biggest edge in Polymarket spread arbitrage isn't knowledge — it's speed and coverage. Manually checking even 50 markets takes hours. Our scanner checks hundreds every minute.
Spreadr was built specifically for this. We scan every active Polymarket contract via the CLOB API, calculate real-time spreads, filter for genuine opportunities (accounting for fees and liquidity), and deliver alerts the moment a profitable spread appears.
Let Spreadr find these opportunities automatically
Real-time scanning across all Polymarket contracts. Instant alerts when profitable spreads appear. Daily digests with top opportunities. We're tracking 117+ opportunities right now.