Both venues list short "Bitcoin up or down" windows that ask the same question and give an exact tie to Up. The differences are in the plumbing. Kalshi's 15-minute markets settle on a 60-second average of CF Benchmarks' BRTI and round each order's fee up to the cent. Polymarket's 5-minute markets settle on a 60-second Chainlink average and round fees to five decimal places, with the same 0.07 × price × (1 − price) taker formula. Across 18,001 Kalshi windows and 36,731 Polymarket windows we checked, both landed Up about half the time, and a spot chart called the close wrong more often on Polymarket (8.88%) than on Kalshi (4.40%).
Which one you can use depends on where you live. Kalshi is a CFTC-regulated exchange open to US residents in most states. Polymarket's international site restricts US users, and Polymarket's US exchange is a separate venue with its own market list and fee schedule, so check what is offered to you before comparing.
| Kalshi KXBTC15M | Polymarket "Bitcoin Up or Down", 5 minutes | |
|---|---|---|
| Window length | 15 minutes, around the clock except Thursday 3 to 5 AM ET maintenance | 5 minutes, around the clock |
| Settlement source | CF Benchmarks Bitcoin Real Time Index (BRTI) | Chainlink BTC/USD data stream |
| Settlement value | Simple average of the 60 BRTI prints in the final minute | 60-second Chainlink time-weighted average (since August 14, 2026) |
| Price to beat | The same 60-second BRTI average before the open (the strike) | The same Chainlink average at the start of the window |
| Exact tie | Resolves Yes (Up) | Resolves Up |
| Taker fee | 0.07 × C × P × (1 − P), order total rounded up to the next cent | 0.07 × C × p × (1 − p), rounded to five decimal places |
| Maker fee | None on this series (fee type "quadratic", checked October 6, 2026) | None; Polymarket lists a 20% maker rebate for crypto |
| Account | US exchange account, dollars | International: crypto wallet, USDC. US: separate Polymarket US exchange |
On one contract at 50¢ the shared formula gives 1.75¢. Polymarket charges 1.75¢; Kalshi rounds the order up to 2¢. At 99¢ the formula gives 0.0693¢. Polymarket charges that; Kalshi rounds the order up to 1¢, which is the whole profit a 99¢ contract can make. On a 100-contract Kalshi order the rounding spreads out to about 0.07¢ per contract at 99¢ and the gap nearly closes. So for small orders at extreme prices, rounding matters more than the venue's headline rate. Try any price and size in the Kalshi fee calculator.
Both venues settle on a 60-second average from an index provider, not on Coinbase or Binance. When we compared a Coinbase/Kraken spot read at the close with each venue's official result, they disagreed on 8.88% of Polymarket windows and 4.40% of Kalshi windows, nearly all of it on close calls. Polymarket's shorter windows put more of them near the line. If you hedge or "arbitrage" one venue against the other, remember that the two settlement averages are different numbers over different time spans, so both legs can lose.
Over the samples in our full comparison study, neither venue leaned Up or Down: both settled Up about 49.9% of the time. On Kalshi, Up won 49.87% of 25,370 windows from January 10 to October 4, 2026. With two and a half to three minutes left, the side Bitcoin was on finished there 87.7% of the time on Kalshi, and the Kalshi ask already priced that in. We publish no Polymarket price figures: our logger recorded Polymarket's displayed price, not an executable ask, and that field failed a basic check.
Kalshi's longer window means fewer, larger moves per window and fewer knife-edge closes; Polymarket's 5-minute window means three times as many decisions per hour, each one closer to a coin flip.
For what bots and alert services for these markets do, see Kalshi BTC 15-minute bots. For what the data says about strategies, see Kalshi BTC 15-minute strategy.
Neither gives better odds in our data: both settled Up about half the time and priced outcomes about right. The differences are access, settlement source, window length and fee rounding. Kalshi rounds each order's fee up to the cent, which costs small orders at high prices the most.
No. Kalshi's 15-minute markets settle on a 60-second average of CF Benchmarks' BRTI; Polymarket's 5-minute markets settle on a 60-second Chainlink average. Both give an exact tie to Up.
Both use a taker fee of 0.07 × contracts × price × (1 − price). Kalshi rounds the order total up to the next cent; Polymarket rounds to five decimal places and pays crypto makers a rebate. Kalshi's KXBTC15M series carries no maker fee as of October 6, 2026.
Not cleanly. The two settle on different index averages over different time spans, so positions that look opposite can both lose, and each leg pays a fee. A spot read at the close disagreed with the official result on 4.40% of Kalshi windows and 8.88% of Polymarket windows in our data.
Polymarket's international site restricts US users. Polymarket runs a separate US exchange with its own market list and fee schedule. Check which markets are available to you before comparing.
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Every signal in our BTC 15-minute feed goes into a public results log and a downloadable CSV, graded against Kalshi's official result, losses included, with nothing pulled.
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These are 15-minute binary prediction-market contracts. Any single window can lose 100% of your stake. They settle on a 60-second index average, not on the exchange chart you may be watching. At high prices a loss costs many times what a win pays, and Kalshi's fee raises the win rate you need above the price. Nothing on this page is financial, investment, or betting advice.
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