Both venues charge a taker fee that peaks near 50¢. Here is the formula CalcMyBets uses, a sports example, and why we only mark a cheaper book when the gap still wins after fees.
A raw 1¢ gap between Kalshi and Polymarket is not a shop. The taker fee sits on the price you click.
CalcMyBets only marks a cheaper book when the all-in cent — ask plus that venue's taker fee — still wins by at least 1¢. That is the whole product. This page is the math behind the Skip.
Both venues use the same curve:
fee per contract ≈ rate × p × (1 − p)
p is the price in dollars (50¢ = 0.50). The p × (1 − p) term is largest at a coin flip and near zero at 1¢ or 99¢.
| Venue / category | Rate we use on the board |
|---|---|
| Kalshi (standard event contracts) | 0.07 |
| Polymarket sports | 0.05 |
| Polymarket crypto | 0.07 |
| Polymarket politics | 0.04 |
| Polymarket geopolitics / world | 0 |
Peak Kalshi taker at 50¢: 0.07 × 0.50 × 0.50 = 1.75¢ per contract. Peak Polymarket sports at 50¢: 0.05 × 0.50 × 0.50 = 1.25¢.
Kalshi rounds the fee up to the next cent on the order, so one contract at 50¢ still costs a full penny of fee. Our board compares the raw formula so a single share and a stack use the same curve. Confirm the live schedule on Kalshi and Polymarket fees before you size a real order. Rates move.
| Price | Kalshi taker (≈) | Polymarket sports taker (≈) |
|---|---|---|
| 10¢ | 0.63¢ | 0.45¢ |
| 25¢ | 1.31¢ | 0.94¢ |
| 50¢ | 1.75¢ | 1.25¢ |
| 75¢ | 1.31¢ | 0.94¢ |
| 90¢ | 0.63¢ | 0.45¢ |
A 2¢ sticker gap at 50¢ can vanish after fees. A 2¢ gap at 90¢ usually survives.
Suppose Arsenal is 58¢ on Kalshi and 57¢ on Polymarket.
Net gap ≈ 1.5¢ toward Polymarket. That clears our 1¢ floor, so the board can print the cheaper book. Flip the raw prices to 58¢ vs 57.4¢ and the same math falls under 1¢ — Skip.
This is not “bet Arsenal." It is “if you already want Arsenal Yes, buy it where the all-in cent is lower."
What −110 means is a fee baked into both sides of a moneyline. Prediction-market vig is a separate taker charge on the fill. You still need your own probability. Strip nothing with the No-Vig Calculator and call it a day — that tool is for two-way sportsbook books. For a ¢ contract, put the ask into +EV and subtract the fee in your head or trust the board's all-in comparison.
Those can wipe a 1¢ shop. If the board says Skip, skip.
On standard event contracts Kalshi charges about 0.07 × price × (1 − price) per contract, rounded up on the order. It peaks near 1.75¢ per contract at 50¢ and shrinks toward 1¢ and 99¢.
Same shape, different rate by category. Sports is typically 0.05 × p × (1 − p). Crypto is often 0.07. Some geopolitics markets are fee-free. Always check the venue page. Schedules change.
We add the taker fee to each ask, then compare. If the all-in gap is under 1¢, the sticker difference is noise. The board prints Skip.
The trading fee is charged when the order fills, not when the event settles. Settlement on these binaries pays $1 or $0 on the share itself.