Cross-platform pricing gaps between Kalshi and Polymarket widened noticeably over the past seven days, opening the cleanest set of arbitrage opportunities we have tracked since the spring election cycle. As of the September 2, 2026 open, at least a dozen contracts covering identical or near-identical outcomes are trading 3 to 7 cents apart, and a handful of exotic markets on Polymarket are pricing tail scenarios that Kalshi’s regulated equivalents have already faded.
Below is our weekly breakdown of where the spreads are, why they exist, and what the disciplined arbitrage playbook looks like right now.
1. Fed September Rate Decision: 4 Cent Spread
The single largest volume mispricing this week sits on the September 17 FOMC contract. Kalshi’s “Fed cuts 25 bps in September” market is trading at 72 cents (72% implied probability), while the equivalent Polymarket contract is at 68 cents. That is a 4-cent spread on a market with over $14 million in combined weekly volume.
The gap has persisted for six trading sessions, which is unusual. Two forces are keeping it open: Kalshi’s US retail flow is heavily long the cut following last week’s soft payrolls print, while Polymarket’s crypto-native user base is discounting the possibility of a hot August CPI surprise on September 11. Neither side is wrong on fundamentals, but the arbitrage math does not care: sell the higher side, buy the lower side, collect the spread minus fees.
2. 2026 Senate Control: 3 Cent Persistent Gap
“Republicans retain Senate majority in 2026” is quoted at 63 cents on Kalshi and 60 cents on Polymarket. The spread is smaller than the Fed contract but far more durable. It has been open for most of August and reflects a structural difference in user bases: Kalshi’s political traders skew slightly more bullish on GOP hold odds, likely due to demographic and geographic differences in who trades on a US-regulated exchange versus an offshore crypto venue.
Traders working this spread should note that both platforms settle on the same real-world outcome (control of the chamber as of the January 2027 seating), so basis risk is effectively zero. The primary friction is funding: Kalshi requires USD collateral, Polymarket requires USDC.
3. Bitcoin Year-End Price Bands: The Widest Gaps
Bitcoin year-end price contracts are showing the widest single-contract spreads on the board, though volume is thinner than the macro markets above.
| Contract | Kalshi | Polymarket | Spread |
|---|---|---|---|
| BTC above $120K on Dec 31 | 41 cents | 48 cents | 7 cents |
| BTC above $150K on Dec 31 | 18 cents | 24 cents | 6 cents |
| BTC above $100K on Dec 31 | 79 cents | 82 cents | 3 cents |
The consistent pattern (Polymarket priced higher on every strike) reflects a well-documented “crypto-native optimism premium” on Polymarket’s Bitcoin markets. It is a real, exploitable edge, though the wider spreads on the higher strikes come with lower liquidity and higher slippage.
4. NFL Super Bowl LXI Winner: Team-Level Mispricings
Both platforms now list futures on Super Bowl LXI, and while the top-tier favorites are within a cent of each other, mid-tier team contracts are drifting apart as the regular season kicks off. The Detroit Lions are quoted at 11 cents on Kalshi and 14 cents on Polymarket. The Baltimore Ravens sit at 13 cents versus 10 cents. Sharp bettors are running paired trades across roughly a dozen NFC and AFC contenders to capture 2 to 4 cents per leg with fully hedged exposure.
How to Actually Capture These Spreads
Arbitrage on prediction markets is not free money, and the operational overhead is real. Three things to keep in mind:
- Fees eat spreads. Kalshi charges up to 7% of profits on winning trades. Polymarket charges no fees on trades but requires gas for on-chain settlement. A 3-cent spread can compress to under 1 cent net.
- Capital efficiency matters. Both legs must be funded independently. A $10,000 arb on a 4-cent spread ties up roughly $20,000 in collateral to earn $400 gross before fees.
- Settlement risk is not zero. Contracts on different platforms occasionally resolve on slightly different criteria. Read the rules carefully, especially for macroeconomic contracts where data revisions can matter.
Where to Trade
Both major US-accessible platforms are running normal operations this week with full order books on the contracts above.
- Trade on Kalshi: US-regulated (CFTC), USD funding, best for macro and political contracts.
- Trade on Polymarket: USDC funding, deepest crypto and sports liquidity, offshore for US users.
For a full comparison of platforms, fees, and available contracts, see our 2026 prediction market rankings.