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Implied Probability Calculator

ODDS CONVERTER · PREDICTION MARKETS · LIVE KALSHI, POLYMARKET, ADI, LIMITLESS, MYRIAD PRICES OR MANUAL ENTRY

Convert a probability, or a live prediction market price, into decimal odds, American odds, and breakeven win rate.

Kalshi, Polymarket, Limitless, and Myriad read a live two-sided price (vig included). ADI Predictstreet contracts are real but currently have no trading volume. Try the Fair Value Calculator for those instead.

What's the probability?

What is a probability-to-odds conversion?

A prediction market price is already a probability. Kalshi's contracts, for example, settle at $1 or $0, so a price of $0.35 means the market thinks the event is 35% likely. Traders and sportsbooks, though, usually talk in decimal or American odds, not raw probability. This converts between the two, and, when the input is a live market, separates out the vig (the exchange's own built-in edge) from the underlying probability.

The formulas

  • decimalOdds = 1 / probability
  • americanOdds = probability ≥ 0.5 ? −100 × p / (1 − p) : 100 × (1 − p) / p
  • breakevenWinRate = probability × 100
  • vig = (yesPrice + noPrice − 1) × 100: only computable with both sides of a live market

Worked example

A market prices an event at 25% (probability 0.25):

  • decimalOdds = 1 / 0.25 = 4.00
  • americanOdds = 100 × 0.75 / 0.25 = +300
  • breakevenWinRate = 25%

You'd need to be right more than 25% of the time for a bet at this price to break even. That's the whole point of converting to a win-rate number instead of staring at odds.

Where the live prices come from

Five independent venues, all public keyless market data: Kalshi (a CFTC-regulated exchange; its crypto category prices BTC/ETH/SOL and other coins' year-end and threshold outcomes directly), Polymarket, ADI Predictstreet, Limitless (on-chain, Base, mostly short-duration 5-minute/15-minute/daily crypto up-or-down contracts), and Myriad (on-chain, Abstract L2; not every market has a Yes/No outcome). This tool reads whichever live price you point it at. It doesn't estimate or invent a probability.

Where to go next

Want to see the market's full implied view of where BTC/ETH ends the year, not just one threshold? Use Market-Implied Odds. Think your own probability estimate beats the market's? Size the bet with the Edge Sizer. No live price to convert yet (the contract exists but hasn't traded)? Compute a theoretical fair value instead.

Use via API or MCP

This calculation is available as a deterministic API call: useful for bots or AI agents normalizing prediction-market prices into a common odds format.

Get API key View API docs

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FAQ
Q.01

How is a market price the same thing as a probability?

Kalshi contracts settle at exactly $1 (YES) or $0 (NO). A contract trading at $0.35 means the market collectively prices the event at 35% likely; that's the definition of an efficient binary market's price.

Q.02

What is the "vig" and why can't I see it with a manual probability?

The vig is the exchange's built-in edge: the amount by which the YES and NO prices sum to more than $1. Computing it needs both sides' prices, which only a live market snapshot has; a manually entered probability is just one number with no counter-side to compare against.

Q.03

Why do American odds sometimes show a plus and sometimes a minus?

By convention, probabilities at or above 50% show negative American odds (you risk more than you win), and probabilities below 50% show positive odds (you win more than you risk), the same convention sportsbooks use.

Q.04

Does this only work for Kalshi crypto markets?

The live-lookup mode reads Kalshi, Polymarket, ADI Predictstreet, Limitless, and Myriad's crypto-price markets. The manual-probability mode works for any probability from anywhere. It's pure math, not tied to one venue.