Can you arbitrage Kalshi and Polymarket? The math and the risks
Sometimes, yes. If Yes on one venue plus No on the other costs less than $1 after both taker fees, the pair pays $1 when both venues settle the same way. Near 50¢, fees take about 3.5¢ per pair, so a 3¢ gap usually loses money. The bigger problem is that "both venues settle the same way" is an assumption, not a guarantee.
This page is information, not investment advice. Every position in it can lose money.
How a cross-venue pair works
A Yes contract pays $1 if the event happens. A No contract pays $1 if it does not. Buy Yes on Kalshi and No on Polymarket US for the same event, and exactly one leg should pay $1.
The pair is worth doing only if:
Yes ask (venue A) + No ask (venue B) + fee A + fee B < $1.00
For US residents, the two venues that matter are Kalshi (KalshiEX LLC) and Polymarket US (QCX LLC). Both are CFTC-designated contract markets that trade in dollars.
The fees you have to beat
Both venues charge takers a fee shaped like rate × contracts × price × (1 − price):
- Kalshi: 0.07, per its fee schedule last updated July 7, 2026. Resting (maker) orders pay nothing in most series.
- Polymarket US: 0.0695, effective September 17, 2026, per QCX's CFTC filing.
Fee schedules change, so check Kalshi fees and Polymarket fees before you trust the numbers below. The fee calculator computes both legs for any price.
Worked example 1: a 3¢ gap that loses money
Kalshi Yes ask is 45¢. Polymarket US No ask is 52¢. The pair looks like 97¢ for a $1 payout. You buy 100 of each as a taker.
| Item | Kalshi Yes | Polymarket US No |
|---|---|---|
| Price × 100 | $45.00 | $52.00 |
| Taker fee | 0.07 × 100 × 0.45 × 0.55 = $1.73 | 0.0695 × 100 × 0.52 × 0.48 = $1.73 |
| Leg total | $46.73 | $53.73 |
Total outlay: $100.47. Payout if both settle the same way: $100.00. You lose $0.47 for certain, before any rounding.
Worked example 2: a 5¢ gap that clears fees
Kalshi Yes ask is 40¢. Polymarket US No ask is 55¢.
- Prices: $40.00 + $55.00 = $95.00
- Kalshi fee: 0.07 × 100 × 0.40 × 0.60 = $1.68
- Polymarket US fee: 0.0695 × 100 × 0.55 × 0.45 = $1.72
- Total outlay: $98.40
- Payout: $100.00, so gross profit is $1.60, about 1.6% on capital
That 1.6% is earned only at settlement. If the market closes in four months, your money sits there for four months. Compare that with what the same cash would earn somewhere safer.
Both examples assume the full 100 contracts fill at the quoted ask. Often they do not. The top of the book may hold only a few dozen contracts, and the next level is worse. Our liquidity and spreads guide shows how to price a fill that walks the book.
Why it is not risk-free
The two venues can settle the same question differently
Each venue writes its own contract terms and decides its own outcomes. Kalshi settles under its rulebook and CFTC-filed contract terms. Polymarket.com uses the UMA optimistic oracle. Polymarket US settles under its own rulebook. Wording that looks identical on a market card can differ in the fine print.
It has already happened. At the February 2026 Super Bowl, Cardi B appeared during Bad Bunny's halftime show, and it was unclear whether she sang. Kalshi's rules did not count dancing or appearing on stage without singing or playing as a performance. Kalshi froze the market and settled at the last traded price: 26¢ for Yes and 74¢ for No. Polymarket's market, resolved through UMA, settled Yes at $1.
A trader holding Yes on Kalshi and No on Polymarket would have collected 26¢ on a pair that cost close to $1. The reverse pair would have collected $1.74. Neither is arbitrage. Both are bets on how two different rulebooks treat an edge case.
Kalshi's rulebook (Rule 6.3) allows settlement at the last traded price when an outcome cannot be determined. Polymarket.com's process can resolve a market 50/50. Neither outcome fits the "one leg pays $1" model. See how markets resolve for more cases.
Capital is locked until settlement
Both legs tie up cash until the market resolves, or until you sell. Selling early means crossing two spreads and paying two more taker fees. On Polymarket.com, a disputed resolution can take days. Polymarket's own docs put a disputed case at about 4 to 6 days.
US users cannot use the international order book
Polymarket.com lists the United States as "close-only": users "can close existing positions but cannot open new ones." Many arbitrage scanners compare Kalshi with Polymarket.com prices. For a US resident, those gaps are not tradable. The relevant comparison is Kalshi vs Polymarket US, and state rules can restrict either one. Check availability by state.
Moving money between venues is slow
Kalshi charges no fee for ACH deposits or withdrawals, but ACH takes days. Debit card deposits can cost up to 2%, which wipes out a 1.6% edge on its own. Kalshi does not support wire withdrawals under $500,000. To react to a gap quickly, you need cash already sitting on both venues, idle most of the time.
Execution risk
You place two orders on two systems. If one fills and the other does not, or the price moves before the second leg executes, you hold a one-sided position. Using a resting limit order to save on fees makes this worse: the cheaper leg may never fill.
A checklist before you try it
- Read both venues' rules for the market: source, deadline, and what happens in edge cases.
- Compute the all-in cost with both fees, not the headline prices.
- Check order book depth at the size you want, on both sides.
- Divide the net profit by the months until settlement.
- Ask what you lose if one venue settles at last traded price or 50/50.
Our live comparison shows current prices for markets listed on both venues. Price-gap statistics show how often gaps are wide enough to matter and how long they last.
FAQ
Is Kalshi and Polymarket arbitrage risk-free?
No. The venues use different rules and settlement processes, and they have settled the same event differently, as with the February 2026 Cardi B halftime market. You also face execution risk, fees and capital locked until settlement.
How big does a price gap need to be to cover fees?
Near 50¢, Kalshi's 0.07 and Polymarket US's 0.0695 taker fees add up to about 3.5¢ per Yes/No pair. A gap smaller than that loses money as a taker trade, before spread and slippage.
Can US residents arbitrage Kalshi against Polymarket.com?
No. Polymarket.com lists the US as close-only, so US users cannot open new positions there. The tradable comparison for US residents is Kalshi vs Polymarket US.
What happens if one leg of the arbitrage doesn't fill?
You are left with a one-sided bet on the event. You can wait, chase the other leg at a worse price, or close the filled leg and pay the spread and fees.