Arbitrage Calculator
Find cross-platform arbs between Polymarket and Kalshi. A 3% gross arb can become a loss after fees — this calculator shows you the real numbers.
Arb Calculator
Platform A — YES
2% fee on net winnings
Platform B — NO
Need $57.14 on NO to lock in the arb
Taker fee: 7% × price × (1 − price)
Resolution (optional, for APY)
$2.75 guaranteed profit
How Prediction Market Arbitrage Works
An arbitrage opportunity exists when you can buy YES on one platform and NO on another for a combined cost of less than $1.00. Since one side always wins (paying $1.00), you lock in a guaranteed profit equal to $1.00 minus what you paid. Example: buy YES at 45¢ on Polymarket and NO at 50¢ on Kalshi. Total cost: 95¢. Guaranteed payout: $1.00. Gross profit: 5¢ per pair.
Why Fees Can Kill Your Arb
The catch is platform fees. Kalshi's taker fee at 50¢ is about 2¢ per contract. On a 5% gross arb, that 2¢ per side (4¢ total) wipes out almost all your profit. A 3% gross arb turns into a guaranteed loss. This is the most common mistake new arb traders make — they see the spread and forget the fees.
How to Use This Calculator
- Enter the YES price on Platform A and which platform it is
- Enter the NO price on Platform B and which platform it is
- Enter your total capital to deploy
- See the gross arb, net arb after fees, optimal stake split, and annualized return
Worked Example
“Will Bitcoin hit $200K by December?” — Polymarket YES is at 38¢, Kalshi NO is at 55¢. Combined cost: 93¢. Gross arb: 7¢ per pair (7.5%). You deploy $1,000. The calculator splits your stake: $380 on YES (1,000 shares) at Polymarket, $550 on NO (1,000 shares) at Kalshi. Kalshi taker fee on NO at 55¢: 7% × 0.55 × 0.45 = 1.73¢ per share ($17.33 total). Polymarket fee on YES win: 2% × 62¢ = 1.24¢ per share ($12.40 if YES wins, $0 if NO wins). Worst-case net profit: ~$40 on $930 deployed = 4.3%. If the market resolves in 30 days, that's about 52% annualized.
Cross-Platform Arbitrage: Sportsbooks vs. Prediction Markets
The most interesting arb opportunities often exist between sportsbooks and prediction markets. A sportsbook might have “Lakers win championship” at +800 (implied 11.1%) while a prediction market has the same event's NO contract at 85¢ (implied 85% No / 15% Yes). If the prediction market implies 15% Yes and the sportsbook implies 11.1%, there's a potential discrepancy — though you need to account for the sportsbook vig before calling it an arb. Use our De-Vig Calculator to strip the vig first.
Common Questions
What's the difference between gross and net arb?
Gross arb is the raw spread: $1.00 minus the combined price. Net arb is what you actually keep after both platforms take their fees. Only the net number matters for your real profit.
How does the stake split work?
The calculator splits your capital so you earn the same profit regardless of which side wins. If the YES contract pays out more per dollar than the NO side, you put less on YES and more on NO, ensuring the guaranteed payout is equal either way.
Can I arb within the same platform?
Yes. If you spot a pricing discrepancy on the same platform (e.g., YES + NO prices that sum to less than $1.00), you can set both sides to the same platform. The fee calculation works the same way.
Is prediction market arbitrage risk-free?
Mechanically yes — one side always resolves to $1.00. But there are practical risks: markets can be voided, platforms can change rules, and if a market resolves ambiguously you might lose on both sides. Execution risk also exists: prices move while you're placing the second leg.
Why show annualized return?
A 2% guaranteed profit sounds modest, but if the market resolves in 3 days that's over 200% annualized. If it resolves in 6 months, it's only 4%. The annualized number helps you decide whether the opportunity cost is worth tying up your capital.
Should I use maker or taker orders?
Maker orders (limit orders) have roughly 4x lower fees on Kalshi. If you can wait for your order to fill, the fee savings can make marginal arbs profitable. But you risk the other side's price moving before your order fills.
Is arbitrage betting legal?
Yes. Arbitrage is completely legal on prediction markets and sportsbooks. You're simply taking advantage of pricing discrepancies between platforms — no different from buying a stock on one exchange and selling it on another. However, some sportsbooks may limit accounts that consistently arb. Prediction market platforms generally have no such restrictions.
How do I find arbitrage opportunities?
Monitor the same market across multiple platforms. Look for cases where YES on Platform A + NO on Platform B costs less than $1.00. The most common arb opportunities appear when one platform is slow to update after news breaks, or when platforms disagree on event interpretation. Speed matters — arbs typically close within minutes.