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Odds Converter

Convert between market price, American, decimal, and implied probability.

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What does this calculator do?

The odds converter translates between the three formats you'll encounter across prediction markets and sportsbooks: American moneyline odds (e.g., −110 or +230), decimal odds (e.g., 1.91 or 3.30), and implied probability (e.g., 0.60 or 60%). Each format encodes the same information — the price of a position — but in ways that are not immediately comparable without conversion.

Prediction markets like Kalshi and Polymarket quote prices as implied probability — a contract at 0.63 costs 63 cents and pays $1 if it resolves YES. Sportsbooks use American or decimal odds. When you're trying to compare a Polymarket price against a sportsbook line on the same event, you need to convert to a common format to see which is offering better value.

Enter any one format and the calculator instantly outputs the other two. The math is straightforward: implied probability = 1 / decimal odds; American odds for favorites = −(probability / (1 − probability)) × 100; for underdogs = ((1 − probability) / probability) × 100. The converter handles edge cases like exactly 50% (−100 moneyline) and near-certainty contracts cleanly.

Note that these conversions assume no vig — they treat the quoted price as the true probability. In practice, quoted prices contain a built-in margin. Use the No-Vig calculator after converting to strip that margin out and find the fair probability on each side.

Frequently Asked Questions

What does implied probability mean?
Implied probability is the win probability embedded in a set of odds, assuming no vig. A −110 moneyline implies the bettor must win 52.4% of the time to break even. A prediction market price of 0.70 implies a 70% chance of resolution YES.
How do I convert prediction market prices to American odds?
A prediction market price p (between 0 and 1) converts to American odds as follows: if p > 0.5, American odds = −(p / (1 − p)) × 100. If p < 0.5, American odds = ((1 − p) / p) × 100. For example, a 0.65 Kalshi contract converts to approximately −186 moneyline.
How do I compare a Polymarket price to a sportsbook line?
Convert both to implied probability using this tool, then use the No-Vig calculator to strip the margin from each. The platform with the lower no-vig price on the side you want is offering better value.
Why do sportsbook odds look different from prediction market prices?
Sportsbooks originated in a context where bettors think in terms of "how much do I risk to win $100" — hence American odds. Prediction markets evolved as financial exchanges where price = probability, so they use decimal format bounded between 0 and 1. Same underlying math, different presentation conventions.