Kalshi vs Polymarket: Why Prediction Market Prices Diverge

Prediction markets have gained popularity as a way to "bet" or invest on real-world events like elections, inflation rates, or sports outcomes. Two of the most prominent platforms are Kalshi (a CFTC-regulated exchange) and Polymarket (a crypto-based platform). But if you compare both, you’ll quickly notice something odd: the exact same event often trades at different prices on each platform—even after fees and currency conversion are considered.

Why does this happen? Let’s break down the concrete, practical reasons, show how the math works, and walk through some real-world examples. This is not financial or betting advice, but a mathematical exploration of market dynamics.

1. How Prediction Market Prices Work

At the core, both Kalshi and Polymarket run markets on yes/no questions. Each “yes” share pays $1 if the event happens, $0 otherwise. The price for a “yes” share (say, $0.60) reflects the market’s estimate of the event’s probability, after accounting for platform fees and other frictions.

Example: 2024 US Presidential Winner

Let’s say both platforms offer a market: “Will Biden win the 2024 US Presidential Election?”

• Kalshi price: Yes = $0.61, No = $0.41 (after fees)
• Polymarket price: Yes = $0.65, No = $0.37 (after fees, USD equivalent from USDC)

So why would a rational participant pay $0.65 for a yes-share on Polymarket when they could (in theory) buy the same bet for $0.61 on Kalshi?

2. Key Factors Driving Price Differences

(A) Platform Fees

Both sites charge fees, but they’re structured differently:

• Kalshi: 2% transaction fee (on buy/sell), 1% settlement fee (on profits)
• Polymarket: 2% trading fee on volume (sometimes lower)

Fees eat into arbitrage opportunities. If you buy on one and sell on the other, you pay fees twice, which can erase most small price gaps. When comparing prices, always factor in all fees—something ArbMonster automates across 20 sportsbooks and major prediction markets.

(B) Currency Friction

• Kalshi: USD only (bank deposits, wire, debit/ACH)
• Polymarket: USDC (crypto stablecoin)

Changing money between platforms is not frictionless:

• Converting USD ↔ USDC incurs exchange fees (typically 0.1–0.5%) and sometimes gas fees.
• Withdrawing from Polymarket requires on-chain transactions, which can be slow or expensive during network congestion.

These costs and delays mean that even if a price gap exists, it may not be profitable (or possible) to move funds quickly enough to arbitrage the difference.

(C) Access and Regulation

• Kalshi: Only available to US residents, KYC required, regulated.
• Polymarket: Accessible globally (except for US persons), only a crypto wallet needed, less regulatory oversight.

Not all participants can use both platforms. So, Polymarket’s price may reflect a global average, while Kalshi’s price reflects US sentiment or access limitations.

(D) Market Depth and Liquidity

• Kalshi: Market makers and institutional participants provide liquidity, but sometimes fills are limited for larger sizes.
• Polymarket: Liquidity comes from user-deposited pools (AMMs). Large trades can move the price more.

If you want to buy $10,000 worth of “yes” on both platforms, the average price you pay may differ due to the liquidity curve. A $0.61 price on Kalshi might only be available for $500 before it moves to $0.62.

(E) Settlement Rules and Timing

• Each platform has its own event wording and resolution criteria. Tiny differences (like how a recount is handled, or what time the event is decided) can affect perceived probability.
• Sometimes, one platform updates rules or resolves markets before the other, introducing short-term price gaps.

3. A Worked Example: Arbitrage Math

Let’s walk through whether a hypothetical price gap can actually be exploited, with all frictions included.

Suppose:

• Kalshi: Yes at $0.59, No at $0.43 (after fees)
• Polymarket: Yes at $0.64, No at $0.38 (after fees, USD equivalent)
• You have $1,000 on each platform, already funded

Step 1: Calculate theoretical arbitrage

Buy “yes” on Kalshi ($0.59), sell “yes” on Polymarket ($0.64):

• Buy 1,000 / 0.59 ≈ 1695 shares on Kalshi
• Sell 1,000 / 0.64 ≈ 1562 shares on Polymarket

But you can’t just instantly offset—redemption for profit only happens after event settles. If Biden wins:

• Kalshi pays: 1695 × $1 = $1,695, minus fees
• Polymarket pays: You owe 1562 × $1 = $1,562 (since you sold "yes")

Net profit: $1,695 - $1,562 = $133 (before fees)

Step 2: Subtract all fees

• Kalshi: Transaction and settlement fees (≈3% total)
• Polymarket: Trading fee (2%)
• USD/USDC conversion: 0.2% per side if you try to centralize profits
• Potential slippage: If the price moves as you fill your orders, actual results deviate

Reality check: After all costs, your $133 theoretical profit might drop to $40 or less, or even negative if the market moves or you fail to fill at posted prices. And that's before considering withdrawal delays or risks.

4. Why Price Gaps Persist

• Not everyone can access both platforms.
• Costs and delays make arbitrage hard to scale.
• Different user bases mean different beliefs and hedging needs.
• Liquidity and settlement quirks affect "real" fillable size.

Prediction markets are not like major stock exchanges with high-frequency trading. Price gaps are a persistent feature, not a bug, of the fragmented landscape.

5. How ArbMonster Tracks These Gaps

ArbMonster scans 20+ sportsbooks, Kalshi, and Polymarket live, net of all known fees and at fillable sizes, to reveal true pricing gaps between platforms. The ArbMonster Learn section has more on the technical details. While these tools automate the scanning and math, they can’t eliminate the underlying frictions (funding, withdrawal, settlement risks) or guarantee profits. But they do make the math transparent.

FAQ

Q1: If the same event is $0.60 on Kalshi and $0.65 on Polymarket, is there a risk-free profit?

Not necessarily. After accounting for all fees, currency conversion, fillable size, and timing risks, most price gaps are much smaller than they appear, and many disappear entirely. Only rarely does a true "arb" survive all frictions.

Q2: Why do prices sometimes converge suddenly?

This often happens when large traders (or bots) move funds and exploit gaps, or when new information arrives and both markets reprice rapidly.

Q3: Can I use ArbMonster to guarantee I’ll make money on these gaps?

No. ArbMonster is a data tool that makes price gaps and market math transparent, but it does not guarantee profits or provide advice. All markets carry risks, and platform access varies by location and regulation.

ArbMonster is a data service. Nothing here is financial or betting advice; markets carry risk, venues have age and jurisdiction restrictions, and you are responsible for verifying everything before acting.