Kalshi Prices the Same Event Higher. Here's the Exact Math.
It's not manipulation. It's fee structure, liquidity, and market category. We'll show you when the gap matters and when it doesn't.
Kalshi can price the same event higher once fee structure is included
Polymarket often looks tighter on liquid fee-bearing markets
Directional comparison based on documented fee structures and live order-book mechanics.
Why the Gap Exists: 4 Reasons
Fee Formula Difference
Kalshi charges 0.07 × P × (1 − P), max 1.75¢/contract at 50¢ markets — applied to both YES and NO buyers. Both sides paying entry fees creates overround above 100%.
Polymarket uses probability-based rates (0.75% at 50¢ sports, 1.80% at 50¢ crypto) denominated as % of payout.
Market Liquidity Depth
Overround reflects bid/ask spread. Thinner markets widen spreads. Kalshi has deeper liquidity on US economic and policy events; Polymarket runs deeper on global events and crypto. The same contract on a thin Kalshi market vs. a deep Polymarket market shows a visible gap even before fees.
Category Fee Rules
Politics and policy markets: zero taker fees, zero maker fees Polymarket now charges up to 1.00% on politics markets (as of March 30, 2026). For a political market, Kalshi may actually be cheaper despite a higher nominal ask price.
Contract Wording Differences
The same event may have different resolution criteria on each platform. A price gap that looks like overround may reflect genuine probability disagreement — not just cost. This is NOT the same as exploitable arbitrage; resolution risk can eat the entire spread.
The Math: Side by Side
Illustrative examples — actual prices change in real time. These show fee structure, not live data.
| Scenario | Platform | Ask Pricing Driver | Fee Note |
|---|---|---|---|
| Fed rate cut (50¢ market) | Kalshi | Taker fee up to 1.75¢/contract | Fee formula peaks at 50¢ |
| Fed rate cut (50¢ market) | Polymarket | Economics: ~1.50% peak | Lower peak for this category |
| Political outcome (50¢ market) | Kalshi | Zero taker fee | Politics = zero fees (cheapest) |
| Political outcome (50¢ market) | Polymarket | Up to 1.00% peak | New category fee since Mar 30, 2026 |
| Crypto direction (50¢) | Kalshi | N/A — not listed | Category restriction |
| Crypto direction (50¢) | Polymarket | Up to 1.80% peak | Highest PM category fee |
When Does the Gap Matter?
✅ When It Matters
- Long-horizon position holds (fees compound over time)
- Near-50¢ markets (where fees are highest for both platforms)
- High-frequency or active trading
- Attempting arbitrage between platforms
❌ When It Doesn't Matter
- Politics markets on Kalshi (zero fees — often the cheapest option)
- Low-probability longshots (fee formula approaches zero at extremes)
- Short-term contracts where the spread is small
- Casual trading where fee differences are negligible
Can You Arb the Spread?
The honest answer: rarely. First, the gap looks larger than it is — Kalshi charges zero fees on politics markets (the most-compared category), so a visible price difference there usually vanishes after accounting for fees. Second, when a real gap does exist after fees, resolution rule differences create serious risk: a contract Kalshi resolves YES may resolve NO on Polymarket if the underlying criteria differ. That risk can exceed the visible spread.
Full arbitrage explainer