Compare · head-to-head
Kalshi vs Polymarket.
Live data, methodology, fee math.
Live side-by-side comparison of Kalshi (CFTC-regulated US exchange, USD) and Polymarket (Polygon-based offshore protocol, USDC). Active contracts, 24-hour volume, average spread, top cross-venue price gaps, Brier-score calibration on the past 90 days of resolutions, fee math, and regulatory posture — refreshed hourly from the SimpleFunctions API.
Kalshi contracts
28746
Polymarket contracts
7305
Cross-venue pairs
29
Refreshed
2026-06-08
Side by side · live
Active universe + market structure.
| Kalshi | Polymarket | |
|---|---|---|
| Active contracts | 28746 | 7305 |
| 24h volume | $21446554 | $24208553 |
| Avg spread (LAS, ¢) | 0.95 | 0.55 |
| Regulation | CFTC-regulated (US) | Offshore (Curaçao) |
| Settlement currency | USD | USDC (Polygon) |
| Min trade | $1 | $1 |
| API protocol | REST + WebSocket + FIX 4.4 (institutional) | CLOB v2 + gamma REST |
| Auth | RSA-PSS signed requests | EIP-712 + Polygon wallet |
| Fee structure | Tiered exchange fees, ~1-7% based on contract | ~2% on winning side |
| US access | Full (regulated) | Restricted (geo-blocked, VPN common) |
| Mobile app | iOS + Android | Web + PWA |
| KYC | Required (US KYC) | Wallet-only (no KYC) |
| Withdrawals | ACH + wire | On-chain USDC |
Live · cross-venue
Top 10 price gaps right now.
Matched markets sorted by absolute price gap between Kalshi and Polymarket. Gaps under ~5¢ usually do not survive fee + conversion friction; 10¢+ on liquid pairs can be tradeable. Full pair table (~29 matched pairs) at /screen.
| Market | Kalshi | Polymarket | Gap |
|---|---|---|---|
| Who will be the Bantamweight Title Holder on Dec 31, 2026?: Merab Dvalishvili | 23¢ | 42¢ | 19¢ |
| Who will hold the UFC Flyweight Title title on Dec 31, 2026?: Joshua Van | 25¢ | 42¢ | 17¢ |
| Who will be the Bantamweight Title Holder on Dec 31, 2026?: Petr Yan | 33¢ | 50¢ | 17¢ |
| Will Trump create a National Bitcoin Reserve before Jan 1, 2027?: Before Jan 1, 2027 | 16¢ | 27¢ | 11¢ |
| Who will be the Middleweight Title Holder on Dec 31, 2026?: Khamzat Chimaev | 11¢ | 18¢ | 7¢ |
| Who will be the Middleweight Title Holder on Dec 31, 2026?: Nassourdine Imavov | 20¢ | 27¢ | 7¢ |
| Who will hold the UFC Flyweight Title title on Dec 31, 2026?: Alexandre Pantoja | 25¢ | 31¢ | 6¢ |
| Who will be the Bantamweight Title Holder on Dec 31, 2026?: Sean O'Malley | 4¢ | 10¢ | 6¢ |
| Who will hold the UFC Flyweight Title title on Dec 31, 2026?: Manel Kape | 5¢ | 10¢ | 5¢ |
| Who will be the Middleweight Title Holder on Dec 31, 2026?: Dricus Du Plessis | 3¢ | 8¢ | 5¢ |
Brier calibration · 90d
Calibration on T-24h price.
Brier score = mean squared error between the price 24 hours before settlement and the realized outcome (1 = correct, 0 = wrong). Lower is better. 0.25 is uninformed; 0 is perfect. Computed from resolved contracts in the past 90 days; re-verifiable via /calibration.
| Brier | Hit rate | Samples | |
|---|---|---|---|
| Kalshi | 0.254 | 74.1% | 625,177 |
| Polymarket | 0.323 | 58.3% | 44,167 |
Fee math · $1000
$1000 trade — what you actually pay.
Indicative fee math for a winning $1000 trade at common contract tiers on each venue. Real fees vary with contract category, tier eligibility, and (for Polymarket) Polygon gas at execution. Not financial advice.
Kalshi (medium-tier exchange fee)
$35
3.5% × $1000
Tiered by contract; major event contracts fall in the 1-7% band. Fees added on top of price.
Polymarket (winning-side fee)
$20
2.0% × $1000
Charged on the winning side at settlement; on-chain USDC denominated, plus Polygon gas (~$0.10).
FAQ
Common questions.
Which is better, Kalshi or Polymarket?
Depends on your context. For US-based traders who need legal certainty plus USD denomination, Kalshi is the only CFTC-regulated option. For maximum global liquidity on flagship contracts (politics, crypto, sports) and tighter spreads on those events, Polymarket typically leads. The cross-venue gap table on this page surfaces the actual price differences right now — pick by current depth and price, not by brand. Both venues are accessible via the SimpleFunctions API in one normalized schema.
What is the difference between Kalshi and Polymarket?
Kalshi is a CFTC-regulated US exchange settling in USD with full KYC, more diverse contract types (weather, economics, flights, interest rates), and FIX 4.4 connectivity for institutions. Polymarket is an offshore Polygon-based protocol settling in USDC with wallet-only auth (no KYC), deeper liquidity on flagship political and crypto events, and lower retail fees but higher US-access friction (geo-blocked).
Can I arbitrage between Kalshi and Polymarket?
In principle yes — matched markets do exhibit persistent cross-venue spreads, and the table above shows the top 10 right now. In practice, true arbitrage requires (a) holding capital on both venues, (b) accounting for fee structures (~3.5% Kalshi / ~2% Polymarket on the winning side), (c) USDC ↔ USD conversion if you want to net out, and (d) settlement timing risk (Polymarket settles on-chain). Spreads under ~5¢ usually do not survive friction; spreads of 10¢+ on liquid pairs can be tradeable.
Which has better calibration — Kalshi or Polymarket?
See the live Brier scores in the calibration section above (computed from resolved markets in the past 90 days). Lower is better. As of this build, Polymarket trends slightly more accurate on T-24h-price calibration than Kalshi on overlapping events, partly because Polymarket's deeper liquidity tightens the price 24 hours before resolution. The numbers here are independently re-verifiable via /api/calibration.
How are Kalshi and Polymarket fees compared?
Kalshi charges tiered exchange fees commonly in the 1-7% range on contract value, applied on top of the bid/ask price. Polymarket charges roughly 2% on the winning side at settlement, paid in USDC. For a $1000 winning trade: Kalshi ~$35, Polymarket ~$20 (plus Polygon gas, typically <$0.50). On losing trades the fee structure differs — Kalshi fees are paid on entry; Polymarket settlement fees only apply to the winner. The fee-math card above shows the side-by-side.
Can I use both Kalshi and Polymarket through one API?
Yes. Aggregator APIs normalize both venues into a single schema. SimpleFunctions exposes CLI commands, /api/public/markets returning Kalshi + Polymarket contracts uniformly, /api/public/cross-venue/pairs returning matched contracts with live spreads, and an MCP adapter for compatible AI-agent hosts. Other multi-venue options include FinFeedAPI, PolyRouter, Prediction Hunt, and Adjacent News — see /compare/prediction-market-apis for the full 11-API comparison.
Is Kalshi or Polymarket more popular for the 2026 election cycle?
Polymarket led the 2024 cycle on absolute volume for the presidential headline contracts, partly because of crypto-native traders pushing flagship questions. Kalshi has grown US-resident retail meaningfully since CFTC approval and now lists overlapping political contracts with deeper US-side liquidity on certain state-level and policy contracts. The /api/public/markets feed lets you query active political contracts on both venues today and compare volume in real time.
Do I need a wallet to use Kalshi or Polymarket?
Kalshi: no wallet — sign up with a US KYC-compliant account, fund with ACH or wire, trade in USD. Polymarket: yes — connect a Polygon-compatible wallet (MetaMask, WalletConnect, etc.), fund with USDC on Polygon, sign EIP-712 requests for the CLOB. Through SimpleFunctions you can read both venues with no auth and no wallet — execution still requires venue credentials at the exchange layer.
Related
Deeper guides + neighboring comparisons.
- Cross-venue edge detection: Kalshi vs Polymarket
Detect price gaps programmatically and decide when they're tradeable.
- Kalshi API quick start — JavaScript and Python
From zero to first authenticated request in 5 minutes.
- Quantitative orderbook analysis for prediction markets
Spread, depth, slippage, and liquidity scoring with working code.
- Polymarket vs Metaculus
Real-money trading vs community forecasting — when each one wins.
- Prediction Market APIs — 11 compared
If you want both venues through one API, here are the options.
Both venues, one API.
SimpleFunctions normalizes Kalshi + Polymarket into a single schema with cross-venue arb pairs, calibration, computed indicators, CLI/API surfaces, and an MCP adapter. Public reads free, no auth required.
curl https://simplefunctions.dev/api/public/cross-venue/pairs?preset=arb