Prediction Market Spread Checker
CROSS-VENUE COMPARISON · KALSHI, POLYMARKET, ADI PREDICTSTREET · LIVE PRICES, NO SIGNAL
Compare the same real-world bet's live price across Kalshi, Polymarket, and ADI Predictstreet, and see the spread between them.
Each row must genuinely be the same real-world bet on a different venue — this tool reads and compares the prices you point it at, it doesn't match events across venues for you.
What is a cross-venue spread checker?
The same real-world bet — "will BTC end the year above $150,000?" — can trade at different prices on different prediction-market venues at the same time. Kalshi, Polymarket, and ADI Predictstreet each run their own independent order book, so nothing forces their prices to match exactly. This tool reads the live price for a bet you specify on 2-4 venues at once and reports the spread between the cheapest and most expensive.
The formula
- spreadPct = mostExpensiveVenue.probabilityPct − cheapestVenue.probabilityPct
Nothing more complex than that — this reads real prices, it doesn't estimate or predict anything. You supply which market on each venue is the same bet; the tool never guesses a match.
Worked example
"Will BTC reach $100,000?"-style bet checked on two venues:
- Kalshi: 1.5%
- Polymarket: 1.05%
- spreadPct = 1.5 − 1.05 = 0.45 percentage points
A real, if small, spread — the kind of gap that only shows up when you actually check both venues side by side instead of assuming they agree.
Why this exists
Checking one venue at a time and trusting it as "the" market price misses real, checkable disagreement between independent order books. This tool exists to make that disagreement visible with one call, not to recommend which side to trade — it reads three independent sources and lets you see for yourself where they diverge.
Where to go next
Just need one venue's price converted into odds format? Odds Converter. One of your venues has no live price yet? Fair Value Calculator.
Use via API or MCP
This calculation is available as a deterministic API call — useful for bots or AI agents that need to check for cross-venue mispricing before quoting a probability.
How does this know two markets on different venues are the same bet?
It doesn't guess — you supply each venue's own identifier for what you've confirmed is the same real-world bet. The tool only reads and compares the prices, it never auto-matches events across venues.
Why would the same bet be priced differently on two venues?
Kalshi, Polymarket, and ADI Predictstreet each run independent order books with their own traders and liquidity. Nothing forces their prices to converge exactly, especially on lower-volume contracts.
What happens if one venue has no live price?
That venue's quote comes back with available:false and a reason (e.g. ADI Predictstreet's crypto contracts currently have no trading volume). The spread is still computed from whichever venues did resolve, as long as at least 2 did.
Is this a signal to trade the spread?
No. It's a price comparison, not a recommendation — same "not an AI estimate" principle as the rest of TradingCalc. What you do with a real spread is your call.