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The Odds Gap Data

Prediction Market Historical Prices

Kalshi, Polymarket US, ProphetX and Novig sports prices since June 4, 2026, fees applied, in the same file as the sportsbooks on the same games and lines.

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Since June 4, 2026: 6,694 games from 21 books. Last game added October 6, 2026.

What's in It

  1. Kalshi, Polymarket US, ProphetX and Novig prices on every scan.
  2. Fees applied wherever the venue charges one.
  3. The same game, market and line as the sportsbooks, side by side.
  4. Earliest and closing exchange prices, with the movement between them.
  5. Known issues marked on the rows they touch, never hidden.

Sample

New York Jets at Chicago Bears, October 4, 2026: Chicago Bears moneyline at each book, earliest captured and closing price.

BookMarketEarliestCloseMovement
KalshiMoneyline-175-190+1.88 pts
Polymarket USMoneyline-193-189-0.47 pts
ProphetXMoneyline-186-176-1.27 pts
NovigMoneyline-194-174-2.48 pts
Bally BetMoneyline-182-190+0.98 pts
BetMGMMoneyline-160-190+3.98 pts
BetOnlineMoneyline-155-185+4.13 pts
BetParxMoneyline-182-190+0.98 pts

Download

The last 7 days, free. No signup, no key.

curl -o prediction-markets.csv "https://theoddsgap.com/api/odds-history.csv?sport=all"

Try it: /data/sample.csv holds every book's prices on one finished NFL game, New York Jets at Chicago Bears. Free, no signup, no key.

Known issues: ProphetX prices before the August 26, 2026 repair and Novig sizes before September 28, 2026 are marked on the rows they touch. Every issue by date is in the notes file.

Questions

Are the prediction market prices after fees?

Yes. Where a venue charges a fee, the price in the file already has it applied, so an exchange price and a sportsbook price mean the same thing. The fee model is written out on our methodology page.

How do Kalshi and Polymarket US prices compare with sportsbooks?

That is what this file is for: every exchange price sits beside the sportsbooks on the same game and line. For today's comparison rather than the history, see prediction markets vs sportsbooks.

How far back do exchange prices go?

To June 4, 2026. Some early exchange prices have known problems, fixed since, and the file marks each one instead of dropping it, so you decide what to keep.