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Polymarket · Kalshi · More soon

The same event, priced twice.

See where prediction markets disagree, and why. Free, no account needed.

Open the terminal freeHow it works

Data from

  • Polymarket
  • Kalshi
  • More venues soon

Spreads

Every event, measured across venues.

Each event is paired by hand across venues and priced side by side. The gap is the difference in yes probability, in percentage points, refreshed every 30 seconds.

  • Sorted by widest gap, so disagreements surface first
  • Filter by politics, economics, sports and more
  • Stale prices are flagged, never quietly mixed in

Widest gaps right now

Movers

Ask why it moved before you ask whether to bet.

When the odds jump, Plax lines the move up against recent headlines for that event, so you can see what the market may be reacting to.

  • Biggest 24-hour moves across both venues
  • Headlines matched to each event's keywords
  • Odds history and gap history on one chart

Biggest 24h moves

Alerts

Tell me when the gap opens.

Pick an event and a threshold. When the two venues drift that far apart, the alert opens. No account, and you can remove it any time.

  • Thresholds from 1 to 20 percentage points
  • One alert per event, checked against live gaps
  • Saved in this browser while alerts are in early access

Close to a 5pp gap

Method

How the gap is measured

Four steps, the same for every event. The full methodology, including known limitations, is on the about page.

  1. 1

    Pair

    We match markets by hand when they ask the same question, resolve on the same date, and use compatible rules. Automatic matching gets this wrong too often.

  2. 2

    Normalize

    Every venue's price becomes a yes probability between 0 and 1, with 24-hour volume in dollars and the time of the last update.

  3. 3

    Compare

    The gap is Polymarket's yes probability minus Kalshi's, in percentage points. A positive gap means Polymarket is more confident.

  4. 4

    Flag stale

    If either price is more than 10 minutes old, the gap is marked stale. A stale gap may simply reflect one venue not updating yet.

FAQ

Questions, answered plainly

Yes. Plax is free to use and there is no account to create. It reads public market data and doesn't sell anything.

The difference between two venues' prices for the same outcome, in percentage points. If Polymarket prices yes at 62% and Kalshi at 57%, the gap is +5.0pp. It is measured on the last traded or midpoint price, so it ignores fees and spreads.

By hand. Each pair is listed in a file in the project and checked for the same question, resolution date and rules. Markets that look alike but resolve differently are left out. See the methodology for details.

Prices refresh every 30 seconds and are usually under a minute old. Each price shows when it last updated, and a gap is marked stale when either side is more than 10 minutes old.

Polymarket and Kalshi today. More venues will be added where markets overlap closely enough to compare.

No. A gap is not a trade recommendation. Venues differ in fees, rules, liquidity and who can use them, and any of those can explain a gap. Read the risk disclaimer.

Follow the gap to the source.

Every paired event, both prices, and the headlines in between.

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