Kalshi vs Polymarket Arbitrage Scanner: Live Price Gaps

The same question often trades at two prices. Kalshi and Polymarket both list the 2026 Senate races, the Fed's next decision, the 2028 nominees and the major sports championships. Their order books are separate, so their prices drift apart. This scanner puts the two side by side for every outcome we can match, every 15 minutes, and shows whether the gap is wide enough to lock in after fees.

How to read the table

Each row is one outcome that both venues list, such as "Democratic Party" in the Senate-control market or "Buffalo" in the Super Bowl market.

• Kalshi bid / ask and Polymarket bid / ask are the best prices someone is currently willing to pay (bid) and accept (ask) for a YES contract that pays $1 if the outcome happens. 62¢ means the market prices the outcome at about 62%.
• Gap is the Kalshi midpoint minus the Polymarket midpoint, in percentage points. +3.0 means Kalshi prices the outcome three points higher than Polymarket.
• Cost to lock is the cheaper of two trades: YES on Kalshi plus NO on Polymarket, or YES on Polymarket plus NO on Kalshi. Holding both guarantees exactly $1 at settlement, whichever way the event goes. Hover the number to see which pair of legs it uses.
• Net per $1 is $1 minus the cost to lock minus both venues' taker fees. Rows where the pair returns at least half a cent more than it costs at the quoted prices are shaded green. Below that, Kalshi's per-order fee rounding and a one-tick price move erase the spread.

Rows are sorted by the size of the gap, widest first.

Why the gaps exist

The two venues have different traders, different funding rails and different rules about who can trade.

• Different users. Polymarket's main order book is global and crypto-funded. Kalshi is a US exchange funded in dollars. News reaches the two crowds at different speeds, and each crowd has its own lean.
• Moving money between them is slow. Selling on one venue and buying on the other means a bank transfer on one side and a stablecoin transfer on the other. That friction keeps gaps open longer than they would last inside one exchange.
• Fees differ. Kalshi charges 0.07 × price × (1 − price) per contract. Polymarket's US app charges 0.0695 × price × (1 − price). Both fees peak near 50¢ at about $1.75 per 100 contracts, so a 2-point gap on a coin-flip market is mostly eaten by fees.

Why most gaps are not free money

A positive net in the table means the quoted prices add up. Before treating it as a trade, check five things.

1. The rules must match exactly. Kalshi and Polymarket write their own resolution rules. A Senate race can settle on the certified result on one venue and on media calls on the other. A "Fed decision" market can define the rate band differently. If the two contracts can settle differently, the "locked" pair can lose on both legs. We list only pairs we have checked, but rules change: read both before you trade.
2. Depth. The scanner uses the best price on each side. If only $40 sits at that price, a larger order fills at worse prices and the gap closes.
3. Your cash is tied up until settlement. Locking 3¢ on a market that settles in 2028 earns about 1% a year. Kalshi pays 3.50% variable interest on cash balances of $250 or more, so idle cash can beat a small locked spread.
4. Polymarket's US app has its own book. The scanner reads Polymarket's main order book. US residents trade on Polymarket's separate CFTC-regulated app, whose prices usually track the main book but can differ. Check the price in the app you actually use.
5. Access. Polymarket's US app is not available in Arizona, Illinois, Massachusetts, Maryland, Michigan, Montana, Nevada or Ohio. Kalshi blocks some market categories in some states. See prediction markets by state.

What the gaps are useful for even when you do not lock them

A persistent gap tells you which crowd disagrees. If Kalshi prices a Democratic Senate at 71% and Polymarket at 69%, a trader who already wants a Democratic position gets it two points cheaper on Polymarket. The scanner answers "which venue is cheaper for the side I already want" for every listed outcome, which matters more to most traders than the rare true arbitrage.

Which markets are included

We pair markets by hand, then match outcomes by name inside each pair: party control of the Senate and House, the competitive 2026 Senate and governor races, the Fed's next two decisions, the 2028 presidential winner and both nominations, and the NFL, NBA, NHL and Champions League champions. We leave out outcomes that both venues price under 3%, where a half-cent move looks like a large gap.

We left out markets where the two venues ask different questions. One example is the Israeli prime-minister market: the two venues word it with different deadlines and settlement terms, and their prices differ by more than 15 points for that reason, not because of mispricing.

Bots and automation

Most people searching for a Kalshi or Polymarket arbitrage bot want software that watches both books and fires both legs at once. Both venues have public APIs: our Polymarket API guide covers authentication and order placement, and Kalshi publishes its trading API openly. Three cautions from watching these gaps:

• The widest gaps are usually on outcomes with thin books, where a bot moves the price against itself.
• Legging risk is real: if one leg fills and the other does not, you hold a naked position.
• Any service that sells a bot with promised returns is selling the bot, not the returns.

Frequently asked questions

Is arbitrage between Kalshi and Polymarket legal?

Buying and selling contracts on two regulated venues is ordinary trading. You need to be allowed to use both. In the US that means Kalshi and Polymarket's US app, in a state where both offer the market.

How often does the scanner update?

Every 15 minutes. Prices on both venues move faster than that around news, so confirm the live price before you trade.

Why does a market show a big gap but a negative net?

The gap compares midpoints. Trading happens at the ask, and the spread between bid and ask plus both fees often exceeds the gap. Net is the number that matters.

Do you earn money from this page?

Polymarket links in the table use our referral code, and we earn a commission if you open an account through them. Kalshi links are plain links. See our affiliate disclosure.

Which venue is cheaper overall?

Neither consistently. Gaps flip direction from market to market and day to day. Our Kalshi vs Polymarket comparison covers fees, funding and regulation in full.