Polymarket & Kalshi Odds - Matched Markets & Price Gaps

See where the two biggest prediction markets disagree. Pulls live odds from Polymarket and Kalshi, pairs up markets that ask the same question, and shows the price gap, plus which markets moved since your last run. Click Start, get results in about a minute. No API key.

Not financial advice. This Actor reports public prices. A gap is not a guaranteed profit (see "Limits").

What you get

The dataset has three row types, set in the type field.

type	What it is	Charged
pair	The same question on both venues, with both prices and the gap	$0.003 (gap-found)
market	One market on one venue: price, bid/ask, volume, liquidity, end date	$0.001 (market-checked)
mover	A market that moved since your last run and is not already a market row	$0.001 (market-checked)

Pair fields

Field	Meaning
question, polymarketQuestion, kalshiQuestion	The question as each venue words it
matchConfidence (0-100)	How sure the matcher is that both ask the same thing, with matchReasons explaining why
polymarketYesPct, kalshiYesPct	Probability of YES on each venue, in percent (bid/ask midpoint, else last trade)
gapPts	Absolute difference in percentage points
higherOn	Which venue prices YES higher
spreadAdjustedEdgePts, edgeDirection	The gap after crossing the bid/ask spread (buy YES on one venue, NO on the other). Before fees. Can be negative or empty
polymarketVolumeUsd, kalshiVolumeContracts, *Liquidity	Size of each market (Polymarket in USD, Kalshi in contracts)
closesAt, *Url	Earliest end date and links to both markets
*ChangeSinceLastRunPts	How far each side moved since your previous run

Market and mover fields: venue, question, yesPct, yesBidPct, yesAskPct, priceBasis, volume, volumeUnit, volume24h, liquidity, closesAt, change24hPts (Polymarket only), changeSinceLastRunPts, isMover, hasMatchOnOtherVenue, url.

3 ways to use it

1. Where do they disagree today? (the default run: about 25 biggest markets per venue plus every gap of 3+ points) {}
2. Only one topic, wider net: {"keywords": ["fed", "rate cut", "cpi"], "minGapPts": 2, "minMatchConfidence": 75, "includeMarkets": false}
3. Scheduled alerts to Slack or Discord (run every 15 minutes, state remembers prices): {"keywords": ["bitcoin"], "moverMinPts": 4, "webhookUrl": "https://hooks.slack.com/services/..."}

Input guide

Field	What to enter	Default	Tip
keywords	Words to look for in market titles	empty (all)	Match is on question, event title and category
categories	Kalshi categories, e.g. Politics, Economics	empty	Polymarket has no category field
minVolume	Skip thin markets	1000	Polymarket in USD, Kalshi in contracts
minGapPts	Smallest gap to report, in points	3	2 finds more, noisier gaps
minMatchConfidence	How sure a match must be	80	Below 70 expect false matches
minProbabilityPct	Ignore long shots near 0% or 100%	3	Removes 0.1% vs 0.4% noise
includeMarkets / maxMarketsPerVenue	Deliver market rows	on / 25	Off = only gaps and movers
scanDepth	Markets read per venue for matching	1000	More = more matches, slower
trackMovers, moverMinPts, maxMovers	Movers since last run	on / 5 / 20	First run has no previous prices
stateStoreName	Where prices are remembered	polymarket-kalshi-odds-state	Use one name per watchlist
webhookUrl	Slack, Discord, Make or Zapier URL	empty	One message per run when something is found

Output example

{
  "type": "pair",
  "question": "Will Alexandria Ocasio-Cortez win the 2028 Democratic presidential nomination?",
  "matchConfidence": 89,
  "matchReasons": ["question words 85% alike", "close the same day of each other"],
  "polymarketYesPct": 17,
  "kalshiYesPct": 13.5,
  "gapPts": 3.5,
  "higherOn": "polymarket",
  "spreadAdjustedEdgePts": 2.7,
  "edgeDirection": "Buy YES on Kalshi + buy NO on Polymarket",
  "closesAt": "2028-11-07T15:00:00.000Z",
  "polymarketUrl": "https://polymarket.com/event/democratic-presidential-nominee-2028",
  "kalshiUrl": "https://kalshi.com/markets/kxpresnomd"
}

Pricing (pay per event)

Event	Price
Market checked (one market or mover row delivered)	$0.001
Gap found (one matched pair at or above your minimum gap)	$0.003

• Default run (about 50 market rows and a few gaps): about $0.06
• Gaps only (includeMarkets: false), 10 gaps: $0.03
• Every 15 minutes for a day, gaps only, about 10 gaps each: about $2.90

Competing Actors charge $0.01 to $0.05 per result. You pay only for rows that are delivered.

Use it with

• Before: nothing needed. Then: Google Sheets, a Slack or Discord channel, or a newsletter.
• Make, Zapier, n8n: trigger on "run succeeded", or set webhookUrl for a direct alert.
• AI agents / MCP: call that_red_bird/polymarket-kalshi-odds with {"keywords": ["election"]} and let the agent summarize disagreements between venues.
• Schedule it every 5 to 60 minutes with the same stateStoreName to catch movers.

FAQ

• Is this financial advice? No. It reports public prices and a heuristic match. You decide what to do with it.
• Is a gap an arbitrage? Not by itself. The two markets can resolve on different rules, close at different times, charge different fees, and have thin order books. spreadAdjustedEdgePts shows the gap after the bid/ask spread, but before fees, deposit costs and slippage.
• How reliable is the matching? It compares wording, numbers and end dates. High scores (85+) with "same numbers" and a close end date are usually right. Always open both links and compare the resolution rules.
• Why are there no movers on my first run? There is nothing to compare with yet. Run it again with the same stateStoreName.
• Why are some markets missing? Only binary Yes/No markets that are open are included. Multi-leg combos are skipped. Markets past their end date are skipped.
• Does it need an account or API key? No. It uses the public Polymarket Gamma API and Kalshi's public market data.

Limits

Prices are snapshots at run time. Volume units differ (USD vs contracts). Kalshi does not give a 24h change, so only Polymarket rows have change24hPts. Some pairs are false matches. No trading, no order placement, no personal data.

Support

Open an issue on the Issues tab. If this saved you time, a short review helps other people find it.