Did you overpay on your last bet?
We archive both exchanges' order books for every matched Kalshi–Polymarket market. Paste what you actually paid — the price, your stake, and roughly when you placed it — and we show what the other venue was charging for the same bet at that moment, after each venue's taker fee. Sometimes the answer is “you left $18 on the table.” Sometimes it’s “you got the best price — nice fill.”
Pick the market you bet on
2 checkable markets
| Market | Kalshi ask | Polymarket ask |
|---|---|---|
| Who will win the next presidential election?Politics | 21¢ | 20.7¢ |
| Who will win the Ballon d'Or in 2026?Other | 60¢ | 58.3¢ |
How the check works
A bet is only checkable when we hold both venues' books, which is why the list above is the matched pairs only. For your moment we interpolate the other venue’s bid and ask between the nearest archived snapshots, price your stake at the ask a buyer would have paid, subtract the one-way taker fee (Kalshi rounds up to the cent; Polymarket doesn’t), and compare the payout if the bet hits. A bet held to settlement pays no exit fee. We show the snapshot times used — no invented precision.
Bet checker FAQ
- Did I overpay on my Kalshi bet?
- Maybe — it depends what Polymarket was charging for the same bet at that moment. Pick the market, type in the price you paid, your stake and roughly when you placed it. The checker reads the other exchange's archived order book at that time, subtracts each venue's taker fee, and tells you whether the same stake would have paid more there.
- Why do Kalshi and Polymarket show different prices for the same bet?
- They are two separate order books with different traders, so the same contract rarely costs the same on both. Small gaps usually die to taker fees: Kalshi charges 0.07 × price × (1 − price) per contract rounded up to the cent, Polymarket 0.06 × price × (1 − price). Gaps worth real money are rarer than they look, which is exactly why it pays to check your own fills.
- What fees does the bet checker include?
- The one-way taker fee on entry only. The checker prices a bet held to settlement, and a held bet pays no exit leg. It never counts deposit, withdrawal or spread costs, and the archived books are coarse snapshots — the number is what the book said, not a fill you were guaranteed.