Same Election Question, Two Different Odds: Predictions.io Launches Free Cross-Venue Comparison Tools
with free fee and odds calculators so traders can see what a price actually costs them.
Prediction markets have never been bigger, or more contested. Kalshi, Polymarket and Polymarket US together posted a record $50.59 billion in combined volume in July, with Kalshi accounting for roughly 74.5% of the total. In the same month, New York City opened a probe into both leading venues, a Washington judge ordered Kalshi to halt most wagers in the state, and the CFTC began an internal review of so-called “mention markets.”
Amid that scrutiny, a simpler question has gone largely unexamined: when two venues list the same question, do they agree on the answer?
Often, they do not. On identically worded midterm markets tracked by Predictions.io, “Blue tsunami in 2026?” was priced at 44.5% on Polymarket and 36.0% on Kalshi. “Blue wave in 2026?” showed 82.5% against 74.0%. Both gaps are 8.5 percentage points — on questions whose wording is identical on the two venues. Across a sample of directly comparable binary markets live on more than one venue, the median gap was more than four points, and nearly half of the pairs differed by five points or more. (Prices as of 05:08 UTC on 28 August 2026; both venues’ live prices are shown side by side on Predictions.io.)
Those gaps matter to anyone quoting a single number. A market priced at 44.5% on one venue and 36.0% on another does not have one “market-implied probability” - it has two, and which one gets cited is arbitrary unless the reader is told both.
Alongside the comparison pages, Predictions.io publishes two free tools:
● Fee Calculator — enter any trade and see the fee, total outlay and effective all-in price on each venue, including Kalshi’s 0.07 × P × (1−P) taker formula and maker discount against Polymarket’s zero-fee standard markets.
Kalshi Fee Calculator — vs Polymarket | Predictions.io
Free Kalshi fee calculator and Polymarket fee comparison: enter any trade and see the trading fee, total outlay, and the effective all-in price on both platforms. Kalshi's 0.07 × P × (1−P) taker formula and maker discount, side by side with Polymarket's zero-fee standard markets.
predictions.io
● Odds Converter — convert American, decimal and fractional odds into implied probability and prediction-market prices, and see the vig-free line.
Odds Converter — American, Decimal, Probability | Predictions.io
Free odds converter: turn American (+150), decimal (2.50) and fractional (3/2) odds into implied probability and prediction-market prices — instantly, in any direction. See why sportsbook odds always add past 100% and what the fair, vig-free line looks like.
predictions.io
A direct venue comparison is available at https://predictions.io/compare/polymarket-vs-kalshi, and live midterms markets at https://predictions.io/lobby/us-politics.
Predictions.io operates no market and takes no position in any contract. It is a data and comparison service, not an exchange, broker or investment adviser.
About Predictions.io
Predictions.io is an independent aggregator of prediction markets, bringing prices from Kalshi, Polymarket and Manifold into a single view so the same question can be compared across venues. It publishes free tools for traders and journalists, including a cross-venue fee calculator and odds converter.
Users can learn more about Predictions.io here: https://predictions.io/
Predictions.io socials: https://bio.site/predictions.io
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This article was originally published on Chainwire
